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‘üan cites the case of 苻堅 Fu Chien, prince of 秦 Ch‘in, who
in 383 A.D. marched with a vast army against the 晉 Chin Emperor.
When warned not to despise an enemy who could command the services
of such men as 謝安 Hsieh An and 桓沖 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 淝 Fei River,
and he was obliged to beat a hasty retreat.
If you know neither the enemy nor yourself, you will succumb in every
battle.
The modern text, represented by the 北堂書鈔 and _T‘u Shu_, has
必敗, which I should be inclined to adopt in preference to 殆 here,
though the _T‘ung Tien_ and _Yü Lan_ both have the latter. Chang
Yü offers the best commentary on 知彼知己. He says that these words
“have reference to attack and defence: knowing the enemy enables
you to take the offensive, knowing yourself enables you to stand
on the defensive.” He adds: 攻是守之機守是攻之策 “Attack is the
secret of defence; defence is the planning of an attack.” It would
be hard to find a better epitome of the root-principle of war.