Well, it's a largely thankless profession, you teach the same things year after year, and probably see kids struggle and fail more often than you'd like...every now and then a prodigy will wander through your class, but even then there's they'll give themselves credit for learning so well instead of respecting you for how well you teach.

I wanted to be a teacher for a long time until I actually talked to my debate coach. I became very close with him, and I knew he was being brutally honest when he told me that, although he enjoys teaching, it becomes tedious after so long. We all know how awesome it is to have the the young and enthusiastic teacher, but as stricter and stricter rules are laid down from politicians who want to make education a political rallying point, parents and students continue to be batshit insane, and you still don't get the salary you deserve? The young, enthusiastic teacher turns into the crabby curmudgeon who couldn't be arsed to care about another generation of students that they're starting to understand less and less.