Can't see any confounding variables here! /s

> Hard work is deliberate practice. It’s not fun while you’re doing it, but you don’t have to do too much of it in any one day (the elite players spent, on average, 3.5 hours per day engaged in deliberate practice, broken into two sessions)

Let's not pretend like 3.5 hours a day of practice is not a lot. I completely agree that this is what it takes to be good, but try doing anything for 3.5 hours a day and then say that you "didn't have to do too much of it".