Invariably, the best practitioners of any artform were born that way.
You can't train to become michael jordan - you don't have the combination of lightning fast reflexes, 20/20 vision, and general game-sense to get there. You can't become the next Usain Bolt - you don't have the high calves, strong tendons, long legs, and insane fast twitch muscle composition to get there. You can't become the next yo-yo ma, you don't have the supportive infrastructure (musicians for parents), and you weren't performing since you were 5. You can't become the next John Carmack, you simply don't have the brains for it.
Along that continuum, we move from scientifically provable limitations, to anecdotes that only those in the specific niche know, but are hesitant to express - some for fear of ridicule and spite (how dare he say that!), some for fear of shame (...).