Whenever that happens, I try to remember something my professor once told me:
You really need to stop thinking that you need to know what you want to do with your life. Because really, you don't.
He's probably right. After all, not all decisions we make are lifelong and crucial. Those are very comforting words to hear from a respected adult in academia, and possibly the best advice I've ever been given.
Another teacher of mine, one with whom I've shared hours of exciting academical banter, once said with a sigh: "Kids these days - you think life is so short. It's not!" This exclamation was prompted by my rant about wanting to read too many subjects and not having the time to do it. These men are both in their forties, and looking at their careers, it's clear that they practice what they preach.
At some point next year, I will be graduating, whether I'm ready for it or not. (Probably not.) I love my studies, but I have no idea what I want to do with the rest of my life. The plan, for now, is to work on my thesis and enjoy the process. And then I guess I'll just have to take it from there.