When a general, unable to estimate the enemy's strength, allows an inferior force to engage a larger one, or hurls a weak detachment against a powerful one, and neglects to place picked soldiers in the front rank, the result must be rout.
When envoys are sent with compliments in their mouths, it is a sign that the enemy wishes for a truce. If the enemy's troops march up angrily and remain facing ours for a long time without either joining battle or removing demands, the situation is one that requires great vigilance and circumspection. To begin by bluster, but afterward to take fright at the enemy's numbers, shows a supreme lack of intelligence.
When the general is weak and without authority; when his orders are not clear and distinct; when there are no fixed duties assigned to officers and men, and the ranks are formed in a slovenly haphazard manner, the result is utter disorganization.
When you know both yourself as well as your competition, you are never in danger. To know yourself and not others, gives you half a chance of winning. Knowing neither yourself or your competition puts you in a position to lose.
Invincibility is in oneself, and vulnerability is in the opponent. Invincibility is a matter of defense, vulnerability is a matter of attack. Therefore skillful warriors are able to be invincible, but they cannot cause opponents to be vulnerable. That is why it is said that victory is discerned and not manufactured.
The skillful tactician may be likened to the shuai-jan. Now the shuai-jan is a snake that is found in the Ch'ang mountains. Strike at its head, and you will be attacked by its tail; strike at its tail, and you will be attacked by its head; strike at its middle, and you will be attacked by head and tail both.
Getting people to fight by letting the force of momentum work is like rolling logs and rocks. Logs and rocks are still when in a secure place, but roll on an incline; they remain stationary if square, they roll if round. Therefore, when people are skillfully led into battle, the momentum is like that of round rocks rolling down a high mountain - this is force.
When the common soldiers are too strong and their officers too weak, the result is insubordination. When the officers are too strong and the common soldiers too weak, the result is collapse.
To perceive victory when it is known to all is not really skilful... It does not take much strength to lift a hair, it does not take sharp eyes to see the sun and moon, it does not take sharp ears to hear the thunderclap.