The 10k hours rule is actually a misunderstanding from a paper on violin practice by Anders Ericsson. An error that the author himself explains in his book Peak: Secrets from the New Science of Expertise. It doesn't mean that you can't learn something to mastery in 10k hours or less. It just means that 10k hours is kind of an invented number. Some skills require more time, some less, but all of them require purposeful practice.