Who would hurt themselves on purpose?
If you get hurt,
No one will notice the catch.
The trick was a success
If a lie seems true to everyone.

The goal of a spy is to sow doubt in the enemy camp. A returned spy is one who confirms the enemy's suspicions about people from his camp. The “self-mutilation” stratagem is to incite strife in one’s own camp. Send to the enemy of your man with whom you are allegedly in a quarrel, so that he offers him an alliance against you. Then you can lull the enemy's vigilance.

During the Spring and Autumn era, the ruler of the Jin kingdom wanted to expand his lands. He was going to attack the small domain of Hu. First, he gave his daughter as a wife to the ruler of this fief.
Then he asked his advisors:
− I want to increase our lands. Who should I win?
“Attack the domain of Hu,” answered one adviser.

The ruler pretended to be angry at this answer:
“We are now related to the kingdom of Hu.” How can you go to war against him? - he cried and ordered the public execution of this adviser.

He told his subjects to execute a criminal sentenced to death instead of his adviser. He decided that he could afford not to treat his man too cruelly. The criminal was dressed in advance in the dress of an adviser and spies were sent to Hu to spread gossip.

The rumor about how the adviser was punished for proposing an attack reached Ruler Hu. He believed that the Jin ruler was now his reliable ally and did not pay attention to military preparations. Soon, King Jin attacked the kingdom of Hu. Thanks to the surprise of the attack, he won an easy and quick victory. With the help of the stratagem, the Jin ruler gained new lands with minimal losses.