It is essential to seek out enemy agents who have come to conduct espionage against you and to bribe them to serve you. Give them instructions and care for them. Thus doubled agents are recruited and used.
When campaigning, be swift as the wind; in leisurely march, majestic as the forest; in raiding and plundering, like fire; in standing, firm as the mountains. As unfathomable as the clouds, move like a thunderbolt.
This does not mean that the enemy is to be allowed to escape. The object is to make him believe that there is a road to safety, and thus prevent his fighting with the courage of despair. After that, you may crush him.
If we know that the enemy is open to attack, but are unaware that our own men are not in a condition to attack, we have gone only halfway towards victory.
There are roads which must not be followed, armies which must not be attacked, towns which must not be besieged, positions which must not be contested, commands of the sovereign which must not be obeyed.
You can ensure the success of your attacks if you only attack places that are undefended. You can ensure the safety of your defense if you only hold positions that cannot be attacked. Therefore, that general is skillful in attack whose opponent does not know what to defend; and he is skillful in defense whose opponent does not know what to attack.
All warfare is based on deception. If your enemy is superior, evade him. If angry, irritate him. If equally matched, fight and if not: split and re-evaluate.