True strength is an insane concept used in martial art storylines: such as movies, video games, and comic books. It really has no basis in
reality.
A perfect example of this is Ryu from street fighter. He wanders the world over searching for true strength. Nothing else in life matters.
Mas Oyama searched for it in the mountain tops in a Korean movie called "Fighter in the Wind."
Daizaemon Kaze in the manga Gantz also searches for true strength.
The closest thing we have to a concept of true strength in
reality is "he got
heart," or "a true soldier."