1.I want to expand my horizons.
2.I've made a tough decision, sir. Here is my resignation.
3。I quit 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 up my resignation at this moment, 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'm quitting because I want to try something different。