When you know both yourself as well as your competition, you are never in danger. To know yourself and not others, gives you half a chance of winning. Knowing neither yourself or your competition puts you in a position to lose.
If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.
Therefore the skillful leader subdues the enemy's troops without any fighting; he captures their cities without laying siege to them; he overthrows their kingdom without lengthy operations in the field.
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.
If our soldiers are not overburdened with money, it is not because they have a distaste for riches; if their lives are not unduly long, it is not because they are disinclined to longevity.
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.
All warfare is based on deception. Therefore, when capable, feign incapacity; when active, inactivity. When near, make it appear that you are far away; when far away, that you are to lure him; feign disorder and strike him. When he concentrates, prepare against him; where he is strong, avoid him. Anger his general and confuse him. Pretend inferiority and encourage his arrogance.
When he utilizes combined energy, his fighting men become, as it were, like rolling logs or stones... The energy developed by good fighting men is as the momentum of a round stone rolled down a mountain thousands of feet in height.
If words of command are not clear and distinct, if orders are not thoroughly understood, the general is to blame. But if his orders are clear, and the soldiers nevertheless disobey, then it is the fault of their officers.
When the enemy's envoy's speak in humble terms, but continues his preparations, he will advance. When their language is deceptive but the enemy pretentiously advances, he will retreat. When the envoys speak in apologetic terms, he wishes a respite. When without a previous understanding the enemy asks for a truce, he is plotting. When the enemy sees an advantage but does not advance to seize it, he is fatigued.