Know the enemy and know yourself; in a hundred battles you will never be in peril. When you are ignorant of the enemy, but know yourself, your chances of winning or losing are equal. If ignorant both of your enemy and yourself, you are certain in every battle to be in peril.

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.

Hence the saying: 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.

Know your enemy and know yourself and you can fight a hundred battles without disaster

It is said that if you know your enemies and know yourself, you will not be imperiled 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 imperiled in every single battle.

(1) He will win who knows when to fight and when not to fight. (2) He will win who knows how to handle both superior and inferior forces. (3) He will win whose army is animated by the same spirit throughout all its ranks. (4) He will win who, prepared himself, waits to take the enemy unprepared. (5) He will win who has military capacity and is not interfered with by the sovereign. 18. Hence the saying: 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.

Know thy self, know thy enemy. A thousand battles, a thousand victories.

"Know yourself and your adversary and you will be able to fight a hundred battles without a single disaster." This Chinese aphorism is as valuable for guerrilla warfare as a biblical psalm.

Know the enemy, know yourself and victory is never in doubt, not in a hundred battles.

If you know yourself but not the enemy, for every victory gained you will also suffer a defeat.

"17. Thus we may know that there are five essentials for victory: (1) He will win who knows when to fight and when not to fight. [Chang Yu says: If he can fight, he advances and takes the offensive; if he cannot fight, he retreats and remains on the defensive. He will invariably conquer who knows whether it is right to take the offensive or the defensive.] (2) He will win who knows how to handle both superior and inferior forces. [This is not merely the general’s ability to estimate numbers correctly, as Li Ch’uan and others make out. Chang Yu expounds the saying more satisfactorily: “By applying the art of war, it is possible with a lesser force to defeat a greater, and vice versa. The secret lies in an eye for locality, and in not letting the right moment slip. Thus Wu Tzu says: ‘With a superior force, make for easy ground; with an inferior one, make for difficult ground.’"] (3) He will win whose army is animated by the same spirit throughout all its ranks. (4) He will win who, prepared himself, waits to take the enemy unprepared. (5) He will win who has military capacity and is not interfered with by the sovereign. [Tu Yu quotes Wang Tzu as saying: “It is the sovereign’s function to give broad instructions, but to decide on battle it is the function of the general.” It is needless to dilate on the military disasters which have been caused by undue interference with operations in the field on the part of the home government. Napoleon undoubtedly owed much of his extraordinary success to the fact that he was not hampered by central authority.] 18. Hence the saying: 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.

To fight an enemy properly, you have to know what they are. Ignorance is defeat.

If you know the enemy and know yourself, you need not fear the result of a hundred battles.

If you know the enemy and know yourself, your victory will not stand in doubt; if you know Heaven and know Earth, you may make your victory complete.