Stress
Don't pull your hair out. In this job, there'll always be something more to grade, more lesson plans to draw up, and new teaching methods to research and try. On the upside, you'll never be bored.
Of course, if you're the kind of person who only gets a good night's sleep when everything in your agenda is checked off in blue ink, teaching will be a tough career. You might need to invest in some hair dye to cover up the gray you're certain to start sprouting. Learning to cope will be about balance, prioritizing, and organizing (so add some sticky notes to your shopping list).
And then there's the little matter of making ends meet and having nightmares about job cuts. Maybe eventually you'll land a contract job, be on track for tenure, and learn to subsist on PB&J's. But here's the good news: According to Forbes magazine, teaching is one of the ten happiest jobs out there, despite all the issues that come with working in education. Stressed? Check. Poor? Check. Happy? Check!