1. I want to expand my horizons.
2. I've made a tough decision, sir. here is my resignation.
3. I'm quitting because I don't want to be stuck in a rut. I want to move on.
4. First of all, I'd like to say that I've really enjoyed working with you. However, I think it's about time for me to leave.
5. I've been trying, but I don't think I'm up to this job.
6. I've been here for too long. I want to change my environment.
7. I'm sorry to bring this up at a bad time, but I've decided to study abroad.
8. To be honest, I've got a better offer.
9. I'm running out of steam. I need to take a break.
10.I quit because I want to try something different.