This question turned up in my Daily Forwards Step. There was also this quote:
You have to find something that you love enough to be able to take risks, jump over the hurdles and break through the brick walls that are always going to be placed in front of you. If you don’t have that kind of feeling for what it is you’re doing, you’ll stop at the first giant hurdle.
This was originally posted at another (now extinct) blog of mine.