Do you agree? Have you experienced the same in your work/life?

TL;DR The article (from Sept 2019) applies the 80/20 rule three times in succession to illustrate that 50% (0.8^3) of consequences come from 1% (0.2^3) of causes. Thus, "I encourage all business owners to ... block three to four hours out of their day ... to work on the A-level tasks and projects that really matter. Avoid distractions"

Not unfamiliar advice with a simple principle: identify and focus on your priorities. That is the heart of the matter, and is why this advice works. David Allen in "Getting Things Done", and other well-known authors and speakers have similar techniques.

Which is to say that it is very likely for someone either to have experienced or to have seen this.