Kill one, terrify a thousand.

It is only the enlightened ruler and the wise general who will use the highest intelligence of the army for the purposes of spying, and thereby they achieve great results.

Those skilled at making the enemy move do so by creating a situation to which he must conform; they entice him with something he is certain to take, and with lures of ostensible profit they await him in strength.

Thus those skilled in war subdue the enemy's army without battle .... They conquer by strategy.

If your enemy is secure at all points, be prepared for him. If he is in superior strength, evade him. If your opponent is tempermental, seek to irritate him. Pretend to be weak, that he may grow arrogant. If he is taking his ease, give him no rest. If his forces are united, separate them. If sovereign and subject are in accord, put division between them. Attack him where he is unprepared, appear where you are not expected.

First learn to become invincible, then wait for your enemy's moment of vulnerability.

Spies are a most important element in water, because on them depends an army's ability to move.