Practice makes perfect? Nope. Correct practice makes perfect? Close. Supervised correct practice makes perfect? Yup. 10,000 of practice makes expert? Nop

Practice makes perfect? Nope. Correct practice makes perfect? Close. Supervised correct practice makes perfect? Yup. 10,000 of practice makes expert? Nope. 10,000 hours of supervised correct practice makes expert? Nope. 10,000 hours of progressively more difficult supervised correct practice makes expert? You got it! Supervised doesn't mean having a teacher standing behind you watching your work. I think it does mean having some degree of feedback on what you are doing and how you are doing it. In the case of coding that could mean having your code critiqued in open-source projects (either explicitly or as a side effect of the process). Then there's the question of what "expert" means in a contextual practical sense. To use a personal example, I was not trained as a machinist. I trained in electronics and software. Yet, I had a need to manufacture parts using various CNC machines, so I learned. Am I an expert? No way. I do, however know I can fabricate nearly any part and, more importantly, in the process developed a great understanding of design for manufacturability. In my own context yes, I am an expert. This did not take 10,000 hours. If I had to guess I'd say less than 1,000 spread over a number of years with an intense focus during a period if approximately six months.