How did you find a satisfying career, and how did you manage to succed in it?

I'm an undergraduate on the dean's list at a relatively prestigious university. In a little more than a year, I'm faced with graduation, and I'm panicked because I need to start planning my next move now, be it a job in the private sector, a PhD program or professional grad school. I have a wide range of options, but I don't know what I want, only that whatever I do, I want to do it well. So for those of you out there that found a career that you enjoy, that you're good at, that's intellectually stimulating, that affords you independence, allows you to advance yourself, or that makes you feel good at the end of the day, tell me, how did you find it, and when did you know that you wanted to do it? How did you find inspiration? How did you find your passion? And how can I find mine? Responses from people who were in my shoes (ambitious, well educated, lots of options and potential) 5-15 years ago are particularly appreciated.

How did you find a satisfying career, and how did you manage to succed in it?
what did you major in for starters?