> The point is that, because of the small number of available slots, professional athletes tend to be the intersection of the sets {people who work the hardest} and {people who are the most genetically gifted}.

And were born during the right months.

That's important because a couple of months of age makes a big difference when you're young. Since you're competing with other folks who also have both genes and work ethic, physical maturity differences can be significant.