There has been a long debate about what variable is a more reliable predictor of success over decades (Cox, 1926). A classic study by Cox (1926) examined the relationship between IQ, achieved eminence, and 67 personality traits. As a result, the group who had achieved eminence had not only a higher IQ but also several distinct personality traits (Cox, 1926). Specifically, Cox (1926) explained, “youths who achieve eminence are characterized not only by high intellectual traits, but also by persistence of motive and effort, confidence in their abilities, and great strength or force of character”, emphasizing the importance of non-cognitive factors as well as the cognitive factors for achievements. Accordingly, various studies have begun to focus on non-cognitive skills as essential for success in diverse areas of life (Akos & Kretchmar, 2017; Carver et al., 2010; Duckworth et al., 2007; Heckman et al., 2006). However, previous studies have more focused on what variable among non-cognitive variables is a more reliable predictor of success rather than identifying the relationship itself between success-related variables. Therefore, the present study empirically investigated the relationships among the success-related variables.

Optimism is one of the non-cognitive factors that have been extensively studied as a predictor of success over the last 30 years (Carver et al., 2010; Scheier & Carver, 1985; Segerstrom, 2007; Tetzner & Becker, 2018). Optimism is most commonly defined and measured as a dispositional personality trait, meaning the generalized expectation of positive outcomes in the future (Scheier & Carver, 1985). It is well known that optimism is associated with positive outcomes in various domains of life. Optimism was found to be correlated with academic achievement (Tetzner & Becker, 2018), and to lead to higher engagement and persistence in achieving academic goals (Carver et al., 2010). In context with career success, optimism is positively correlated with work-related outcomes such as higher income (Segerstrom, 2007).

Adolescence is a key period for the development of optimism. Dispositional optimism is generally conceptualized as a personality trait that is relatively stable and consistent over time and context (Carver & Scheier, 2014). However, several studies have supported the social-cognitive perspective, in which personality traits such as optimism are not fixed and invariant due to heredity effect, but rather a cognitive process determined by interaction with environmental factors (Atienza et al., 2004; Tetzner & Becker, 2018). Tetzner and Becker (2018) reported the stability of optimism was only 0.33 in early adolescents who had recently transitioned to secondary school. Also, adolescence is expected to experience psychosocial demands, such as social roles, which can affect personality development. Orejudo et al. (2012) reported that relationships with family and peer groups of adolescents who are undergoing personal and socialization development processes can contribute to the development of optimism. Moreover, given that adolescents go through identity development and maturation to set life goals for their future, optimism can play an important role, especially in adolescents.

In sum, it has been verified that optimism could predict success in diverse areas of life (Carver et al., 2010; Segerstrom, 2007; Tetzner & Becker, 2018). Also, optimism can be changed by environmental factors and adolescence in which individuals experience substantial life changes is the key period for developing optimism. Having said that, does developing optimism in adolescence ensure unconditional success in personal life? Although there is no doubt that optimism contributes to the increased possibility of successful personal life, it is hard to claim that there is a specific factor, as a sole predictor of success, that may guarantee success. It is because a person’s successful growth and development have complex causal relationships between diverse variables, whether at the biological, psychological, or social levels, in which the individual is embedded (Napolitano et al., 2021). However, most studies on exploring success-related variables focused on what variable is a more reliable predictor of success rather than identifying the relationship itself between the variables. There are only a few studies that explored the relationship between success-related variables, especially with optimism, which has been studied as a predictor of success. Therefore, this study aims to clarify the relationship itself between optimism and success-related variables in adolescence.

In the last few years, grit is one of the non-cognitive skills that have been the most focused as a predictor of success in adolescence. Grit refers to “perseverance and passion for long-term goals” (Duckworth et al., 2007, p.1087). Duckworth et al. (2007) investigated why some people achieved better or succeed even though they have a similar level of intelligence. The investigation found that successful people have something in common; they make persevere ‘effort’ for and show consistent ‘interest’ in achieving their goals without giving up even if they fail or suffer in the process (Duckworth et al., 2007). Grit is composed of two elements, which are ‘perseverance of effort’ and ‘consistency of interests’. The former indicates the ability to maintain effort toward long-term goals despite hardships and failure. The latter implies the ability to maintain interest in long-term goals despite hardships and failure (Duckworth et al., 2007). It has been demonstrated that grit can be changed by environmental factors such as proper intervention (Alan et al., 2019; Cross, 2014), and the impact of such factors is especially greater in adolescence, the key period in which people experience substantial life changes.

The previous studies on grit focused on the positive effects that the trait has in various domains of life. A seminal work in this field, Duckworth et al. (2011), examined the practice process of students who participated in the National Spelling Bee and investigated which students performed better. The result demonstrated students who devoted more time to deliberate practice performed better in the final competition even though they evaluated the process as more effortful and less enjoyable than other kinds of preparation activity (Duckworth et al., 2011). Lam and Zhou (2019) systematically reviewed the empirical findings over the past 10 years on the relationship between grit and academic achievement and found that there was a positive association between grit and academic achievement. Grit is also known as a predictor of outstanding success in other various and challenging domains. Duckworth et al. (2007) investigated among cadets who enrolled in at the U.S. Military Academy, West Point, to find out which cadets excel in their training. The result showed that grit was incremental predictive validity of success than any other factor (SAT score, high school rank, or self-control) in the first year of West Point (Duckworth et al., 2007). Also, a study of Eskreis-Winkler et al. (2014) showed that grit is a superior predictor of retention in workplace sales, high school, and marriage.

As previous studies demonstrated, optimism and grit are both predictors of success in various domains. Then, how do the two variables associate with each other? Surprisingly, although many studies reported a significant correlation between optimism and grit (Oriol et al., 2020; Tuckwiller et al., 2017), the causal direction of the correlation between the two variables has not yet been clearly discussed. There are only a few studies that investigated the mechanism of the relationship between the two variables (Oriol et al., 2020; Tuckwiller et al., 2017). Oriol et al. (2020) examined whether grit and self-control could mediate the relationship between optimism and life satisfaction in adolescents. The result showed a mediating effect between grit and life satisfaction and the absence of mediation with self-control (Oriol et al., 2020). In other words, optimism is more associated with the ability to persevere in pursuing long-term goals, which is a component of grit, than self-control one’s rather immediate gratification. However, previous studies on optimism and grit were biased toward certain cohorts such as adults or specific groups (Duckworth & Eskreis-Winkler, 2013; Tuckwiller et al., 2017). Therefore, considering that adolescence is the key period for developing optimism and grit, the current study sought to explore a mediator in the relationship between optimism and grit among adolescents.

Recently, growth mindset has received the attention of many studies as a predictor of grit (Duckworth, 2016; Snipes et al., 2012). Growth mindset represents one’s belief in the malleability of personal attributes (mindset) can shape a person’s worldview, goals, and behavior. In other words, people with growth mindset believe that personal attributes, including their intelligence, can grow through their effort and education. In contrast, people with the fixed mindset believe that personal attributes are biologically or environmentally determined and cannot be changed through their effort and education (Dweck, 2006). Thus, it seems quite reasonable that holding different beliefs in the same situation can yield huge differences in how an individual reacts (Dweck, 2017). This is because when people believe that their efforts will bring valuable outcomes in various areas, they are more likely to set grit which is long-term goals and persist to achieve them. Duckworth (2016) suggested that growth mindset can lead to grit, Snipes et al. (2012) also reported that growth mindset was one of the strongest contributors to grit. Also, the correlation between growth mindset and grit has been proven by studies using brain imaging technology. Both variables appeared to be linked to brain regions involving cognitive-behavioral control but functioning differently, which implies that grit and growth mindset are closely related in a neurological sense, and growth mindset might play an essential role in cultivating grit (Wang et al., 2018).

Growth mindset can be an important psychological resource, especially in adolescence. It was found that students with growth mindset showed higher academic achievement than students with fixed mindset (Blackwell et al., 2007; Claro et al., 2016). Claro et al. (2016) investigated growth mindset and academic achievement of high school students across all of the socioeconomic strata in Chile. The study found that the growth mindset strongly predicted academic achievement, and these findings were found across all socioeconomic classes of the country. In addition, the growth mindset was found to have a significant buffering effect on the negative impact of poverty on achievement (Claro et al., 2016). Beside this, Yeager et al. (2019) reported that in a large sample of US adolescents (n = 12,490), growth mindset intervention improved performance of underachieving students and could lead to an overall increase in enrollment in mathematics courses.

Optimism could play an essential role in developing growth mindset. Binning et al. (2019) investigated the effectiveness of an intervention program to improve growth mindset targeting American adolescents, and a significant effect was found only for students who have high educational expectations. In other words, having no expectations in the future education can make the belief that one can grow meaningless or insignificant. On the other hand, few studies empirically examined the relationship optimism and grit (Dardick & Tuckwillber, 2019; Tuckwiller et al., 2017). For example, Dardick and Tuckwillber (2019) demonstrated a direct path from optimism to growth mindset for undergraduate and graduate students, where optimism was found to be a higher-order factor reflecting broader expectations than growth mindset. Also, a pilot study by Tuckwiller et al. (2017) found a linear relationship between optimism and growth mindset in adolescents with learning disabilities. However, the authors mentioned that the sample size of the pilot study was small (n = 17), so follow-up studies are needed to be replicated with larger samples (Tuckwiller et al., 2017). Therefore, the current study aimed to examine the role of optimism as a potential factor that can contribute to improving growth mindset based on sufficient sample size.

Based on the previous studies described above, this study aims to explore the association with optimism, growth mindset, and grit. Also, the current study attempted to analyze the mediating effect of growth mindset on the relationship between optimism and grit and discover the psychological mechanism of the association between optimism and grit.

Based on the previous studies discussed above, optimism seemed to be linked to grit and growth mindset could influence the relationship between optimism and grit. Thereby, the current study sought to investigate the relationship between optimism, growth mindset, and grit among Korean adolescents. Specifically, this study focused on the mediating effect of growth mindset in the relationship between optimism and grit. The following research questions were explored:

  1. 1.

    Does optimism predict grit of adolescents?

  2. 2.

    Does growth mindset predict grit of adolescents?

  3. 3.

    Does growth mindset mediate the relationship between adolescents’ optimism and grit?

Regarding these questions, we expect that optimism would positively predict grit and growth mindset would positively predict grit among adolescents. Also, this study was designed to explore the mediating role of growth mindset in the relationship between optimism and grit in adolescence. In doing this, the relations among the major success-related variables can be examined comprehensively and thereby empirically verified the paths among them, which make good contributions to the body of knowledge for future research. In addition, it is expected that the investigation of the effect of optimism as an antecedent factor that can improve growth mindset and grit can be utilized in specific educational programs or intervention plans.

Method

Participants

Participants were 647 adolescents (342 male and 305 female; male 52.9%) from South Korea and most of the participants resided in Seoul (48.4%) and Gyeonggi (18.9%) province. The age of participants ranged from 12 to 16 years with an average age of 14.26 (SD = 1.3; 12-year-olds n = 91, 13-year-olds n = 106, 14-year-olds n = 137, 15-year-olds n = 171, 16-year-olds n = 142).

Measures

Optimism

Optimism was assessed through the Korean version of the Life Orientation Test-Revised (LOT-R; Scheier et al., 1994; Shin et al., 2005), which measures an individual’s generalized sense of future expectations. The LOT-R is composed of 10 items: 3 positively worded items (e.g., “In uncertain times, I usually expect the best”), 3 negatively worded items (e.g., “I hardly ever expect things to go my way”), and 4 filler items not used in scoring. The respondents indicated the extent to which they agreed with each of the items on a 5-point scale from 1 (not at all like me) to 5 (very much like me). A total score was calculated by reverse scoring the negatively worded items and combined with the positively worded item’s scores. The higher the total score, the higher the level of optimism. The Cronbach’s alpha in Shin’s (2005) study was 0.73, and 0.69 in the current study.

Growth mindset

Mindset beliefs were measured using the Korean version of the Theories of Intelligence scale (Dweck, 1999; Lee & Kwon, 2016) to assess students’ beliefs about the malleability of intelligence. The scale consists of 6 items, which contain two subscales: 3 items for growth mindset (e.g., “I can always greatly change how intelligent I am”) and 3 items for fixed mindset (“I have a certain amount of intelligence, and I really cannot do much to change it”). The respondents indicated the extent to which they agreed with each of the items on a 6-point scale from 1 (not at all like me) to 6 (very much like me). To create sum scores, fixed mindset items were reverse-coded and combined with growth mindset items. Accordingly, higher sum scores were associated with higher level of growth mindset. The reported Cronbach’s alpha for the full scale was 0.78 (Blackwell et al., 2007). In the current study, the Cronbach’s alpha for the full scale was 0.87.

Grit

Grit was measured by the Korean version of the Original Grit Scale (Grit-O; Duckworth et al., 2007; Park et al., 2020) assessing the ability of individuals to sustain effort and maintain consistency of interests. The Grit-O scale consists of 12 items: 6 items for measuring consistency of interest (e.g., “My interests change from year to year”) and 6 items for measuring perseverance of effort (e.g., “I have achieved a goal that took years of work”). The respondents indicated the extent to which they agreed with each of the items on a 5-point scale from 1 (not at all like me) to 5 (very much like me). Items for consistency of interest were reverse calculated so that higher scores represent high levels of grit. The Cronbach’s alpha in Duckworth et al. (2007) was 0.85 (Consistency of Interests, α = 0.84; Perseverance of Effort, α = 0.78), and 0.68 (Consistency of Interests, α = 0.62; Perseverance of Effort, α = 0.70) in the current study.

Procedure

Before data collection, all procedures were reviewed and approved by Seoul National University’s Institutional Review Board (IRB No. 1608/003–012). The study was conducted in the Developmental Psychology Lab at Seoul National University. After participants arrived in the lab at the scheduled time, they were escorted to a quiet room. Parents provided consent for students to participate, and students assented to participate in accordance with the purpose of the study and the storage of data. Also, they were informed about directions that there were no right or wrong answers and that responses would remain anonymous were noticed to participants. Trained staffs collaborated in the recruitment of the participants, sharing a paper–pencil survey on demographic information and self-report questionnaires of optimism, growth mindset, and grit in 20 min.

Data analysis

Collected data were statistically analyzed by using SPSS (version 26.0). First of all, we computed the means, standard deviations, and ranges of the variables (optimism, growth mindset, and grit) for descriptive statistics of the study. Second, to examine the association between optimism, growth mindset, and grit, we conducted Pearson’s correlation analysis. Also, mediating analysis of growth mindset on the relationship between optimism and grit was investigated using model 4 of PROCESS macro version 4.1 developed by Andrew Hayes (2018). Finally, bootstrapping was performed to verify the statistical significance of the mediating effect.

Results

Descriptive statistics of the variables used in the study are shown in Table 1. The mean of optimism was 21.4 (SD = 3.4) with the score range of 12 to 30. The mean of growth mindset was 23.8 (SD = 5.5) with the score range of 6 to 36. Finally, the mean of grit was 36.6 (SD = 5.2), with the score range of 23 to 50. The means of each subscale were as follows: consistency of interest (M = 17.0, SD = 3.3) and perseverance of effort (M = 19.6, SD = 3.4).

Table 1 Descriptive statistics of optimism, growth mindset, and grit
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The correlations between optimism, growth mindset, and grit are provided in Table 2. The results suggest that all variables significantly correlated with each other. Optimism was positively correlated with growth mindset (r = 0.35, p < 0.01) and grit (r = 0.33, p < 0.01). Also, a significant positive correlation was found between growth mindset and grit (r = 0.21, p < 0.01). At the subscale level, consistency of interest (r = 0.16, p < 0.01) and perseverance of effort (r = 0.35, p < 0.01) both were positively correlated with optimism. Also, growth mindset was positively correlated with consistency of interest (r = 0.13, p < 0.01) and perseverance of effort (r = 0.20, p < 0.01).

Table 2 Correlations between optimism, growth mindset, and grit
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The mediating effect of growth mindset on the relationship between optimism and grit was investigated. As shown in Table 3, all the structural paths were statistically significant. Optimism had a significant and positive impact on growth mindset (B = 0.57, p < 0.001). Growth mindset had a significant and positive impact on grit (B = 0.10, p = 0.006). Also, the total effect (B = 0.50, p < 0.001) of optimism on grit was significant. When including the mediation variable, growth mindset, the direct effect of optimism and grit weakened remaining significant (B = 0.44, p < 0.001). These results indicated a mediating role exists, in which growth mindset partially mediated the relationship between optimism and grit. In addition, we used a bootstrapping analysis of PROCESS macro to verify the significance of the mediation effect. The bootstrapping procedure was accomplished on 5,000 samples with 95% confidence intervals. As shown in Table 4, the mediating effect of growth mindset on the relationship between optimism and grit was statistically significant (bootstrap 95% CI = 0.015 – 0.107).

Table 3 Test results of the mediating effect of growth mindset in the relationship between optimism and grit (including consistency of interest and perseverance of effort)
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Table 4 Bootstrap test of the mediating effect of growth mindset
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Following the same procedure, the study also tested the mediating effect of growth mindset on the relationship between optimism and two components of grit separately. First, growth mindset had no significant impact on consistency of interest (B = 0.05, p = 0.05) as shown Table 3. The total effect (B = 0.15, p < 0.001) and the direct effect (B = 0.12, p = 0.002) of optimism on consistency of interest were statistically significant. Also, bootstrapping was applied to test the mediation effect. As presented in Table 4, the results showed that there was no significant mediating effect of growth mindset on the relationship between optimism and consistency of interest (bootstrap 95% CI = -0.001 – 0.060).

Furthermore, we tested the mediating effect of growth mindset on the relationship between optimism and perseverance of effort. As shown in Table 3, all the structural paths were statistically significant. In detail, growth mindset had a positive and significant impact on perseverance of effort (B = 0.05, p = 0.028). Total effect (B = 0.35, p < 0.001) and direct effect (B = 0.32, p < 0.001) of optimism on perseverance of effort was statistically significant. Also, the mediating effect of growth mindset on the relationship between optimism and perseverance of effort was statistically significant (bootstrap 95% CI = 0.003 – 0.060).

Discussion

The present study was designed to examine the relationship among the major non-cognitive variables that predict success. To be more specific, we investigated how optimism is associated with grit and the mediating effect of growth mindset on the relationship between optimism and grit in adolescence. The two components of grit were additionally analyzed. The main results of this study can be summarized as follows.

First, optimism in adolescence directly predicted grit. This indicated that the higher the adolescents’ optimism level, the higher their grit turned out to be. The result was consistent with previous studies that reported significant correlations between optimism and grit, and optimism positively predicted grit (Duckworth & Eskreis-Winkler, 2013; Oriol et al., 2020). In a similar vein, it was reported that optimistic people were more prone to make an effort and commitment to achieve their goals (Kleiman et al., 2017), which reflects important aspects of grit (Duckworth et al., 2007). Tang et al. (2019) suggested that promoting goal commitment can strengthen grit in adolescence. However, it does not mean that optimistic people commit themselves to every goal and value it highly. Rather, they tend to adjust their cognitive behavioral regulation by increasing engagement in their goals of a higher priority, while diminishing participation in their goals of a lower priority (Geers et al., 2009). In other words, optimistic people judge objectively where their resources should be invested to pursue their goals leading to higher expectations and values. Also, in the hierarchical framework of goal, grit was associated with superordinate goals, which coupled with exceptional achievements that often require long times (Duckworth & Gross, 2014). Therefore, optimistic people’s expectations of the future can serve as a mechanism for achieving long-term goals (Oriol et al., 2020). Taken above together, this study found empirical evidence that adolescents’ optimism can affect grit.

Second, the adolescent’s growth mindset positively predicted grit. This finding supported the second hypothesis of the current study, which means that the higher the level of growth mindset, the higher the level of grit. It is also in line with previous findings that growth mindset and grit are significantly related to each other, and growth mindset plays an important role in developing grit levels in adolescence (Dweck, 2017; Snipes et al., 2012). The results of this study were also supported by the previous theoretical proposition that the belief in the malleability of individual attributes would determine their subsequent behaviors (Dweck, 2017). This is because when people believe they can improve their abilities through their efforts could encourage them to sustain their passion despite difficulties. In addition, growth mindset was related to goal setting, goal operation, and goal monitoring which had a positive effect on the perseverance of effort and goal achievement (Leondari & Gialamas, 2002). Otherwise, Zhang et al. (2022) conducted cross-lagged analysis of the relationship between growth mindset and grit in a large sample of Chinese elementary school students. It was found that grit predicted rank-order increase in growth mindset and higher growth mindset also predicted rank-order increase in grit, mutually reinforcing each other (Zhang et al., 2022). The present study confirms previous findings and contributes additional evidence that suggests growth mindset can positively affect grit.

In addition, the current study examined the relationship between growth mindset and both components of grit. As a result, growth mindset positively predicted perseverance of effort but did not positively predict consistency of interest. This result could be interpreted in relation with several studies that confirmed consistency of interest and perseverance of effort may have different outcomes (Datu et al., 2016; Disabato et al., 2019). Recently, Disabato et al. (2019) found perseverance of effort was positively and strongly correlated with subjective well-being, beliefs about well-being, and personality strengths, while consistency of interest was weakly and negatively correlated with them. In the same context, Datu et al. (2016) reported that perseverance of effort predicted positive affect and life satisfaction, but consistency of interest did not. The result of this study contributes to providing additional evidence of the role of growth mindset as a predictor of perseverance of effort, expanding existing knowledge of previous studies with the two components of grit that focused on the predictive effects thereof.

Third, growth mindset partially mediated the relationship between optimism and grit. This finding showed that as levels of optimism increased, growth mindset enhanced, which in turn improved grit that is perseverance and passion for long-term goals. The results of our study coincide with previous findings that optimism can lead to an increase in growth mindset and grit (Tuckwiller et al., 2017). However, the previous study on adolescents with learning disabilities conducted by Tuckwiller et al. (2017) had a small sample size (n = 17), so the finding seems to be difficult to generalize. Taking this into account, the current study offered valuable insights with a large sample of adolescents. Our study also found empirical evidence on direct effects in which both pathways, from optimism to grit and from optimism to growth mindset, were significant. In other words, one’s expectation of a positive future can increase the belief in which intelligence can grow and improve through their effort. This result has confirmed the findings of Dardick and Tuckwillber (2019) which found a direct pathway from optimism to growth mindset among college and graduate students, and that of Binning et al. (2019) which reported the effect of interventions to improve growth mindset was significant only for students with high educational expectations. According to the expectancy-value theory, the fundamental mechanism of growth mindset predicting diverse successes depends on the degree to which an individual’s expectations of successful results and evaluation of value (Thomas et al., 2019). Therefore, students’ positive expectations for a specific task would affect successful outcomes through growth mindset. The current study sheds light on the role of optimism by confirming the result that optimism may well function to develop growth mindset as well as grit.

Additionally, we analyzed the mediation effect of growth mindset in the relationship between optimism and the two components of grit, consistency of interest and perseverance of effort, respectively. Our findings showed that growth mindset partially mediated optimism and perseverance of effort. In contrast, growth mindset has no significant mediating effect on optimism and consistency of interest. This indicates adolescents’ optimism would enhance growth mindset which might subsequently lead to the perseverance of effort rather than the consistency of interest. It is because growth mindset and grit are conceptually related in terms of the way to react to challenges and setbacks by maintaining an effort toward long-term goals rather than maintaining an interest toward long-term goals. As reviewed earlier, our results supported the previous findings that the two components of grit were found to generate different outcomes (Datu et al., 2016; Disabato et al., 2019).

This study has mainly three limitations. First, this study used self-reported questionnaires to measure optimism, growth mindset, and grit. The responses may be affected by participants’ social desirability, response biases, and other factors. Therefore, it is expected that future studies may reduce the errors of measurement adopting different research methods and enhance the research reliability. Second, this study is limited by its research design, cross-sectional analysis, by which the causal relations among variables may not be clearly revealed. Previously, optimism was regarded as a stable personality trait (Scheier & Carver, 1992), but it was also discussed that optimism could be changed by environmental factors. For instance, childhood adversities were associated with decreasing optimism (Korkeila et al., 2004). Thus, our cross-sectional exploration of the impact of optimism in adolescence, a period with many physical, psychological, and environmental changes, may not be insufficient. Therefore, follow-up studies are needed to verify whether the causal relationship between each variable is supported by using longitudinal data. Third, variables not considered in our study might have some influence on the results. For example, optimism may be affected by gender, adversities during childhood, parental-child relationship, and peer group (Boehm et al., 2015; Korkeila et al., 2004; Tetzner & Becker, 2018; Ek et al., 2004), and growth mindset may also have different outcomes by gender (Dweck, 2006). Considering this, further studies need to be carried out to systematically examine the relevance among variables in consideration of more diversified personal and environmental factors.

Despite the limitations, the findings of this study have a number of important implications for future research. First, our findings in the present study examined the relations among the major predictors of success and thereby empirically verified the paths among them which is a step further approach prior studies that mainly explored success-related variables focusing on what variable is a more reliable predictor of success. In particular, this study offered valuable insights by conducting analysis on nationally representative Korean adolescents. It is because prior studies on optimism, growth mindset, and grit had low generalizability due to the focus on rather narrow subjects such as novice teachers (Duckworth & Eskreis-Winkler, 2013) and adolescents with learning disabilities (Tuckwiller et al., 2017). Accordingly, the present study verified the mediating effects of the growth mindset in the path from optimism to grit, with nationally representative Korean adolescents and this result is more generalizable. Moreover, adolescence is an important period to build various psychological skills for a positive and constructive life. Our findings shed new light on promoting optimism in adolescence and can be a starting point leading to improvement in various success-related variables. Therefore, developing optimism needs to be included as a key factor in education and intervention programs targeting adolescents. Lastly, to our knowledge, this study is the first empirical study to investigate the mediating effect of growth mindset on optimism and grit in Korean adolescents with a large number of samples and to analyze both components of grit respectively, and thereby identify specific mechanisms.