That anecdote is from a book called Art and Fear, by David Bayles and Ted Orlando. It's a short, excellent study on the exact thrust of this thread: i.e, the collision of talent and persistence and how a successful artist harnesses both of them.

On talent they say, "By definition, whatever [talent] you have is exactly what you need to produce your best work. There is probably no clearer waste of psychic energy than worrying about how much talent you have -- and probably no worry more common."

Which to me sums up the topic nicely.