Yeah but just because you have two legs, it doesn't mean that you're going to win the 400m relay in the Olympics if you keep trying... Having two legs barely scratches the surface; even in the extremely unlikely case that you actually make it to the Olympics, you have to account for the fact that your personal success depends more on your team's performance than on your own performance.

Everybody and everybody's mum has a 'prepared mind'. The kind of basic level of intelligence that's required for earning a billion dollars is extremely common among the general population. Billionaires are not geniuses; they have slightly above average intelligence and/or skill.

The pool of people who have 'slightly above average intelligence and/or skill' is massive. Hundreds of millions of people. On the other hand, the pool of people who are billionaires is tiny in the thousands. It's easy to see why it's a lottery.