This TED talk by Mihaly Csikzentmihalyi about creativity and flow made me think about what actually determines greatness in life, both from an individual perspective and from a agency perspective.
It all comes down to one thing: experience. Intelligence and talent is one thing, but becoming super-skilled is all about doing things many times over. After ten years of doing something, you will fully master it. So, it's all about statistics. Nassim Nicolas Taleb, author of Fooled by Randomness, has an even more extreme position: he argues that success is totally random – people who have reached exceptional wealth have been the right people at the right time in the right environment.
I'd say the outlook for somebody who believes only in statistics is rather gloomy, and I believe there's one way to beat the system: productivity (not really surprising, most exceptional people I know also happen to work a lot). So, if you're twice as productive as the average person, you will do twice as much and instead of ten years, you'll master a subject after five years. If you're lazy, things will take longer – unless you're a lucky bastard, that is.