This advice surprises me. With one foot in the classical music world when I was younger, there are absolutely music skills that take many years if not decades to get to 90% on. And those that have put the work in are absolutely and obviously competent.
Similarly, when I'm working with someone who started off as a machinist, then a designer, then went to school and became an engineer, I find it baffling to think that I can absorb 90% of their knowledge in 6 weeks.