Resignation Pro

What's a good reason to put on your resignation letter?

I'm quiting my part time job because it's too stressful and the pay isn't worth it. (I have another full time job that I'm keeping). What reason should i put on my resignation letter or if my employer asks why I'm quitting. I don't want to say that the job is too stressful and the pay isn't worth it. I want to leave in good terms and at the same time, I want to sound professional in my resignation letter.

Public Comments

1. "I'm having a baby"
2. I would flat out tell them that they don't pay me enough to put up with their bullshit.
3. I have resigned before and it was pretty difficult as the job was shit and it was for family friends... A good one is that you need to use the time to look after someone who is sick, like a parent or sibling . Or you are relocating or you want to study which will take up all your time....
4. "Personal". Or, you could put "To pursue other career interests".