I realised when I attended university. Not in America of course. Where I live University is very rough. I always had very good grades without any effort. Never needed to study. This gave me a false sense of superiority.
University sent me to rock bottom. I was barely passing tests and since I never had a need to self discipline, studying was just a very complicated thing for me to do. I barely graduated but with the degree I have, no one cares about how you got it, just that you got it so I'm fine.
But seeing people easily getting good grades on all these exams made me realize just how ordinary I am. I guess leaving that teenage view of self centredness behind you is part of growing up.