The Art of War by Sun Tzu

All warfare is based on deception. 18. Hence, when able to attack, we must seem unable; when using our forces, we must seem inactive; when we are near, we must make the enemy believe we are far away; when far away, we must make him believe we are near. If your opponent is of choleric temper, seek to irritate him. Pretend to be weak, that he may grow arrogant. supreme excellence consists in breaking the enemy’s resistance without fighting. 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. To secure ourselves against defeat lies in our own hands, but the opportunity of defeating the enemy is provided by the enemy himself. What the ancients called a clever fighter is one who not only wins, but excels in winning with ease.