1. You're getting sick.
2. Your values aren't met.
3. You're not challenged.
4. No room for advancement.
5. You feel belittled.
6. Your friends notice something's wrong.
7. The company is in trouble.
8. Your relationship with your boss/coworkers has been damaged beyond repair.
9. You dread going to work every day.
10. Family circumstances.
11. It's an emotionally abusive environment.
12. A better opportunity comes along.

Regards