I have what one of my teachers calls the "itty bitty shitty committee" in my head. To me nothing I do is ever good enough, and you can never really achieve perfection in art. The harder I try, the more negative shit my teachers and classmates will have to say about my work.
The only stressful thing is, no matter how good I am, even if I'm the best in all of my classes I know there's someone else out there who is like ten times better than me, easily.