Frustration with certain courses or frustrations of not truly knowing what you want to do with your life(which major you want that really really truly interests while making sure that degree would be any useful at all for the workforce).
I'll admit, I've had that thought tons of times just because I easily get frustrated with math and science courses, despite that I love to use logic and do problem solving, along with my passion for computer software and hardware(both which require a rigorous amount of math). Even though math was never my strongest subject, I never hated it. I just get very frustrated with not being able to pick up the concepts of them at the pacing that I want. I just feel that math and science are just one of those subject where you just HAVE to be naturally gifted with problem-solving skills and logic or math in order to be good while a person who is not naturally gifted, will never just get significantly better.
Another thing that causes me to have thoughts of giving up on college are tuition fees and not always being able to afford them. It's bad enough already to have to pay a lot of money for a stupid campus parking ticket, along with constantly job hunting for another part-time job that consistently fits with my class schedules, paying additional $100s, sometimes nearly a $1000 for textbooks and important items for certain classes and constantly worrying about grade and personal issues outside of school and work.
Anyways, I have thoughts about quitting college out of frustration multiple times but at the same time, I try to look back and tell myself that I don't want to be stuck living with my parents and be a burden to them for the rest of my life nor do I want to end up in a boring, poorly-paid and poorly-managed job.