Grappling. Brazilian Jiu-Jitsu specifically. I'm a purple belt (middle belt, halfway to black belt) and I understand things about manipulating how another human

Grappling. Brazilian Jiu-Jitsu specifically. I'm a purple belt (middle belt, halfway to black belt) and I understand things about manipulating how another human body moves that would either make my white belt mind of 8.5 years ago explode or it would be incomprehensible. It usually takes around 10 years for a person to go from white belt to black belt if they train consistently. There are exceptions, of course, but I usually liken the thought and mat time spent, knowledge acquired, and skills sharpened to obtaining a PhD.