I think it's meant as a convenient "rule of thumb" in juxtaposition to the more commonly known "10,000 hour rule" (which also has some controversy[1]). They are

I think it's meant as a convenient "rule of thumb" in juxtaposition to the more commonly known "10,000 hour rule" (which also has some controversy[1]). They are just saying you can be pretty good at something with 2 less orders of magnitude than mastery. 1. http://www.fastcodesign.com/3027564/asides/scientists-debunk-the-myth-that-10000-hours-of-practice-makes-you-an-expert http://www.fastcodesign.com/3027564/asides/scientists-debunk...