Sun Tzu, answered from the texts and cited to the page.
Foreknowledge — that is the hinge on which the whole art turns.1 The wise sovereign and the good general conquer because they know what ordinary men do not know.1 Know the enemy and know yourself, and a hundred battles hold no terror; know yourself but not the enemy, and for every victory you will pay a defeat; know neither, and you will succumb in every battle.2
That is the full measure of what ignorance costs. But knowledge of the enemy's dispositions can only be obtained from men.3 It cannot be read in omens or drawn from the heavens. The ruler who grudges a hundred ounces of silver in honours to his spies, while armies face each other for years and the decision falls in a single day, commits the height of inhumanity — for he spends his soldiers' lives to save what a single informed man could have given him cheaply.4
From foreknowledge flows everything else. Keep your own dispositions invisible while discovering the enemy's, and your forces remain concentrated where his must be divided.5 Then the victorious strategist seeks battle only after the victory has been won; the man destined to defeat fights first and looks for victory afterward.6 The one wins by making no mistakes — by conquering an enemy already defeated before the first blow falls.6
That is what the art is: not the love of battle, not the glory of the charge, but the patient, exact work of knowing — so that when you move, you cannot lose.
what enables the wise sovereign and the good general to strike and conquer, and achieve things beyond the reach of ordinary men, is foreknowledge.The Art of War
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.The Art of War
Knowledge of the enemy's dispositions can only be obtained from other men.The Art of War
Hostile armies may face each other for years, striving for the victory which is decided in a single day. This being so, to remain in ignorance of the enemy's condition simply because one grudges the outlay of a hundred ounces of silver in honours and emoluments, is the height of inhumanity.The Art of War
By discovering the enemy's dispositions and remaining invisible ourselves, we can keep our forces concentrated, while the enemy's must be divided.The Art of War
the victorious strategist only seeks battle after the victory has been won, whereas he who is destined to defeat first fights and afterwards looks for victory.The Art of War