As technology scaling shrank MOSFETs substantially below the 1 micrometer mark, we started to notice many weird things. Current did not flow in the amount we expected. The transistor did not saturate when expected. The drain sometimes acted like a gate, turning on the channel on its own. Current flows through the oxide, threshold voltage varies wildly over time and with different terminal conditions. But all this strangeness is tolerable as long as we understand why it happens and how to deal with it.