Part II contains this Dustin Moskovitz quote: A lot of graduating students think I just want to work on the hardest problems. If you are one of these people, I predict that you're going to change your perspective over time. I think that's kind of like a student mentality, of challenging yourself, and proving that you're capable of it. But as you get older, other things start to become important, like personal fulfillment, what are you going to be proud of, what are you going to want to tell your kids about, or your grandkids about, one day.

I guess I never grew up, then. I still want to work on the hardest problems. That's what I would want to tell my kids about :-)