Such a rule-of-thumb needs a crucial caveat (said by others better than I'll say it here): You need N years of steadily, deliberately advancing full-time work.
There's a fundamental difference between gaining 10 years of experience, and gaining 1 year of experience 10 times.
It's harder than one might think to sustain continual real advancement over such a period; generally the employer paying the bills needs us to occasionally "take one for the team" and do scut-work for a while, simply due to normal business unpredictability; or the work dries up completely and you have a hiccup while you start somewhere new.
A source of work where opportunity continuously keeps up with ability is a precious thing.
The other caveat is that you have to be concentrating and paying attention to your performance for those 10,000 hours.
Very few people, if any, have the metacognition and executive function abilities to pay attention and steadily improve for 8 hours a day. The experts in Outliers and the research it's based upon would typically practice for only 4-5 hours/day and then rest, or do fun stuff like playing through pieces or doing a few flips or easy jumps. A bunch of anecdotal evidence from myself and my friends in Ph.D programs or professional jobs, plus RescueTime's survey of YC founders, also supports that most people can get no more than 4-5 hours of cognitively demanding work in per day. Hence the 10 years = 10,000 hours.
When you're working an 8 hour day, it's usually more like 4-5 hours a day of heavy concentration, plus 3-4 of overhead (checking e-mail, responding to e-mail, doing grunt work like unit tests that you already know how to do, talking to coworkers, sitting in meetings). If you're lucky. For many senior devs it's 8 hours of talking to people and zero coding.
(Although you can turn that into deliberate practice as well. For a while, shortly before and after I made Senior SWE at Google, I was spending the vast majority of my time answering questions from my peers and doing code reviews. I had very little time for coding and my basic coding skills improved very little, but I got really good at being able to dive into an unfamiliar codebase, identify what people were trying to accomplish, and find a way to make it happen in a not-completely-gross fashion. That skill proved invaluable later on, and basically saved the launch of one high-profile Google product.)
There's a fundamental difference between gaining 10 years of experience, and gaining 1 year of experience 10 times.
It's harder than one might think to sustain continual real advancement over such a period; generally the employer paying the bills needs us to occasionally "take one for the team" and do scut-work for a while, simply due to normal business unpredictability; or the work dries up completely and you have a hiccup while you start somewhere new.
A source of work where opportunity continuously keeps up with ability is a precious thing.