If ignorant both of your enemy and yourself, you are certain to be in peril.

To a surrounded enemy, you must leave a way of escape.

Attack him where he is unprepared, appear where you are not expected.

If the enemy opens the door, you must race in.

A kingdom that has once been destroyed can never come again into being; nor can the dead ever be brought back to life.

Invincibility lies in the defense; the possibility of victory in the attack.

Generally in war the best policy is to take a state intact; to ruin it is inferior to this.