There's a difference between ambition and direction. I think many twenty-somethings have a lot of ambition, and no idea what to apply it to. I know I did at one point.
Not being a twenty-something any more, I'd say I now think it probably almost doesn't matter. Pick something, and work hard at it for a long time.
More correctly I think that 20-somethings with ambition, but no passion, will eventually realize they have no passion and will get sad.
I know lots of fellow recent-grads who are ambitious (in the "I want to be successful!" sense), but have no idea what success really entails for them personally. I've been blessed with a love for hacking, and I don't think what I want to be good at was ever a really big question. For many people, though, it is.
I know fellows who've graduated from engineering or computer science, yet despise code. These are the guys who are truly stuck in a quarter-life crisis: a job they don't care for, and lack of passion to succeed. For most of them their only direction is to try and make management - they don't care about the code anyways, and the financial success will numb their sadness a little bit. I don't think they will find the solution to their "quarterlife crisis" there though.
Not being a twenty-something any more, I'd say I now think it probably almost doesn't matter. Pick something, and work hard at it for a long time.