eachers deal with so much more than delivering the curriculum. There are discipline issues, extra duties before and after school, lesson planning and grading that follow you home, parent phone calls, meetings... Those are just the physical issues.
Why teachers quit should be something every would-be teacher should ponder before taking out loans to pay for college. You don't want to be one of the 44% of newbies who quit within the first five years, because then what will you do with all that...