We can go on and on about how they were lucky and it would all be true. The fact that they were born where and when they were, the connections that fell in to place, etc. are all opportunities they were afforded. But you still can't have the success that Warren Buffet and Bill Gates had without also being incredibly talented and hard working. You could then go on to say that they were born with higher than normal ability (another form of luck). However, it all just sounds so cyclical. So I'll leave you with one of my favorite quotes which I think boils it down very simply:

“Luck Is What Happens When Preparation Meets Opportunity" -Lucius Seneca (Roman Stoic Philosopher)