It is said that if you know your enemies and know yourself, you will not be imperilled in a hundred battles; if you do not know your enemies but do know yourself, you will win one and lose one; if you do not know your enemies nor yourself, you will be imperilled in every single battle.
Sun Tzu
Becoming the enemy means thinking of yourself as if you are in the opponent’s body.
Miaymoto Musashi
To know your enemy, you must become your enemy.
Attributed to Sun Tzu