Sun Tzu says:
One who knows the enemy and knows himself will not be in danger in a hundred battles.
One who does not know the enemy but knows himself will sometimes win, sometimes lose.
One who does not know the enemy and does not know himself will be in danger in every battle.
Zap Says
Know your enemy, know yourself and you hold the keys to victory. That's what it says in Sun Tzu's Art of War and Zapp Brannigan's Big Book of War