As you pointed out, luck sometimes has a lot to do with it, and nobody ever should deny this. As someone who has been in on several startups, sometimes you're in the right place at the right time and sometimes you aren't. If you know the history of Microsoft, this even applies to Bill Gates. Of course, once the luck hands you an opportunity, the rest of it comes into play.

Bringing it down to simple basics, I think the main difference between successful people and those who aren't is that the former believe that their actions make a difference, what you do or don't do is important, that success is possible, and that when you fail, you keep trying. It's no guarantee. Nothing is. But while every person with this attitude is not successful, almost everyone who has earned a lot of wealth has this attitude.

A survey of people I read once showed that whether their parents were wealthy, or dirt poor, parents who instilled this optimistic and pro-active world view into their children was the one thing most of them had in common.