If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.
Sun TzuAgainst those skilled in attack, an enemy does not know where to defend; against the experts in defense, the enemy does not know where to attack.
Sun Tzu