According to a July 14, 2014 article in The New York Times, practice may contribute only 20-25% of the edge needed to reach an elite level of performance. A 1993 study, by contrast, places that factor at 80%.
I have to say that I still think 20-25% is a significant percentage.
Read the article and see how you react.
The last paragraph, in my opinion, says it all:
But in the end, the most important factor over which people have control — whether juggling, jogging or memorizing a script — may be not how much they practice, but how effectively they use that time.