When I'm asked to give career advice, I say four things:
#1 Focus. You have to choose to be great at something very specific, probably more specific than you'd like. I'd love to be good at more things. But you can't focus on too much, as mastery requires a ridiculous level of hard work.
#2 Hard work (grit). To achieve mastery, you have to outwork others in your field. You need roughly 10,000 hours to master a craft and that's just the ticket to play. Gladwell writes eloquently about this-- there are no exceptions, even among the Mozarts, Einsteins, Kobes, Gates, and Jobs.
#3 Passion. Given the required level of focus and hard work, you have to love your craft. I've never met an exception to this rule.
#4 Course correction. Paths to success are messy, not merely emerging from the logging of 10,000 hours of focused, passionate work, but from making good lifetime choices against a backdrop of tradeoffs, ambiguities, and complexities.
Now I'm looking back over this list. It sounds hard. But I'd say great results typically come only with great effort.