Procrastination.

No matter how much you're dreadfully avoiding that one thing, just do it as soon as you can. In the end, you'll be a much happier person than the irritable and frantic person procrastination can form you into. Because as I write about all the reasons not to procrastinate, I really should be studying for finals. So if I'm not going to listen to my own advice, at least you should. Don't procrastinate, it's just not worth it.