"If we know that our own men are in a condition to attack, but are unaware that the enemy is not open..." — Sun Tzu

Now the reason the enlightened prince and the wise general conquer the enemy whenever they move and their achievements surpass those of ordinary men is foreknowledge.

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.

Hence that general is skilful in attack whose opponent does not know what to defend; and he is skilful in defense whose opponent does not know what to attack.

For them to perceive the advantage of defeating the enemy, they must also have their rewards.