10000 hours of practice

Scientifically speaking, 10,000 hours is not a precise figure but shorthand for “lots and lots of dedicated practice”. Even 10,000 hours of dedicated practice may not be enough to give you the skills of a virtuoso. But whether you dream of playing at the concert hall, wielding the guitar, or taking part on the running track, 10,000 hours is a good starting point. Double that and you may even be winning international competitions.

Reference: gladwells-10000-hour-rule-myth

Rebuttal:
There are other factors, genetics, talent etcbottom line 10000 rule will work when following the rule: Nurture That Which is in Your Nature.
In other words,  You can start focusing on what matters. When you find yourself picking up some skills more quickly than others, you learn where to invest your efforts. When you focus your strengths, then you start to find purpose.

Reference: 10-000-hour-myth-why-deliberate-practice-isnt-enough-to-succeed