3. Attack by Stratagem
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.
Li Ch`uan cites the case of Fu Chien, prince of Ch`in, who in 383 A.D. marched with a vast army against the Chin Emperor. When warned not to despise an enemy who could command the services of such men as Hsieh An and Huan Ch`ung, he boastfully replied: "I have the population of eight provinces at my back, infantry and horsemen to the number of one million; why, they could dam up the Yangtsze River itself by merely throwing their whips into the stream. What danger have I to fear?" Nevertheless, his forces were soon after disastrously routed at the Fei River, and he was obliged to beat a hasty retreat.
Chang Yu said: "Knowing the enemy enables you to take the offensive, knowing yourself enables you to stand on the defensive." He adds: "Attack is the secret of defense; defense is the planning of an attack." It would be hard to find a better epitome of the root-principle of war.