Spies cannot be usefully employed without a certain intuitive sagacity.

Against those skilled in attack, an enemy does not know where to defend; against the experts in defense, the enemy does not know where to attack.

Know thy self, know thy enemy. A thousand battles, a thousand victories.

A sovereign of high character and intelligence must be able to know the right man, should place the responsibility on him, and expect results.

If you know both yourself and your enemy, you can win a hundred battles without a single loss.

If the enemy leaves a door open, you must rush in.

On dispersive ground, therefore, fight not. On facile ground, halt not. On contentious ground, attack not. On open ground, do not try to block the enemy's way. On the ground of intersecting highways, join hands with your allies. On serious ground, gather in plunder. In difficult ground, keep steadily on the march. On hemmed-in ground, resort to stratagem. On desperate ground, fight.