The Gladwell book is so bad it's laughable. It's a gross misrepresentation of the work of Anders Ericsson, with completely unfounded extrapolations. So bad it prompted Ericsson to get a non-academic writer to work with him to write his own popular science version of his work, which is titled "Peak". Outliers is the worst example I know of of popular authors bending facts to make a narrative they want to tell. In a nu…
> (ie the Beatles example is complete bullshit, gigs are not practice) Why doesn't that count as practice?
The learning psychology field often differentiates practice from deliberate practice, where practice is just about anything and deliberate practice is focused learning.
In deliberate practice, you have to work at near your skill level, you need to apply proven learning methods, it should take maximal effort, you need a feedback mechanism to course correct, etc. A great deal of focus goes into creating effective mental models and intentionally removing ineffective mental models. It requires good coaching. As you progress in expertise, your practice should involve more risks and failures. (And there's still much more to be said here)
Gigging and noodling aren't going to make for efficient practice as it likely won't be full concentration, won't involve feedback, won't involve challenging material at your skill level, etc.
Also, you can spend 10,000 hours jamming alone in your bedroom on same set of guitar tabs and make shockingly progress compared to someone who spends just a few hundred hours intensely studying music books with a metronome and tape recorder.