There’s a book that says mastery in any field comes after 10,000 hours of practice. The question arises: practice of what?
When it comes to technique, some of that time has to be spent in the “crucible” — which is to say, performance at your highest level. (Not noodling around playing background music for a tea party, or drilling Segovia scales while watching House.) In the crucible your body will produce an adaptive response. You can try to simulate the crucible by practicing with all your might, but it doesn’t work as well as the real thing.
I’ve probably mentioned this before, but one of the things Rey de la Torre told me was that Segovia used to go straight back to his hotel after a concert to work out technical matters while the iron was still hot, while Rey would grab some friends and go out on the town after a concert.
I know from my own experience that an hour giving a solo concert in front of a large and attentive audience was worth 10 hours of playing in a noisy restaurant, and worth 20 hours of practice. Maybe more. And that if I would go home and work on my guitar playing right after a good performance, while I was still hot, my results were always much better for it.
Intensity, not extensity, leads to the adaptive response. I’d fill that 10,000 hours with plenty of intensity