The enemy's spies who have come to spy on us must be sought out, tempted with bribes, led away and comfortably housed. Thus they will become double agents and available for our service. It is through the information brought by the double agent that we are able to acquire and employ local and inward spies. It is owing to his information, again, that we can cause the doomed spy to carry false tidings to the enemy.
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.
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.
In all fighting, the direct method may be used for joining battle, but indirect methods will be needed in order to secure victory. In battle, there are not more than two methods of attack.. the direct and the indirect; yet these two in combination give rise to an endless series of maneuvers.
There are not more than five musical notes, yet the combinations of these five give rise to more melodies than can ever be heard.There are not more than five primary colors, yet in combination they produce more hues than can ever been seen.There are not more than five cardinal tastes, yet combinations of them yield more flavors than can ever be tasted.
For the wise man delights in establishing his merit, the brave man likes to show his courage in action, the covetous man is quick at seizing advantages, and the stupid man has no fear of death.