The cult of genius can be very caustic to young minds, especially in mathematics. I used to do some rather stupid things out of a combined sense of pressure from family, teachers, and peers. I would compare myself unfairly to historical luminaries as a yardstick of what I should be accomplishing at what age. I worked incredibly hard, but on intractable problems and not on reasonable pieces of research for even a precocious mathematician. My grades suffered because I thought I was going to solve some open conjecture instead of learn the tools bit by bit like virtually every other successful mathematician had done before me.
Depression can set in when you discover that your 20th birthday has passed and you are not Evariste Galois. I know it sounds stupid when it is phrased like that but human psychology is full of improbable behavior designed around avoiding cognitive dissonance. We're funny meatbots.