This is an episode from the Three Kingdoms. Cao cao sent a letter to Zhou Yu to summon him to surrender. Zhou Yu tore Cao's letter to pieces. Zhou Yu's classmate, Jiang Gan, was working for Cao Cao as an adviser, Jiang offered to travel to Wu to persuade Zhou Yu to surrender. One day while Zhou Yu was discussing with his subordinates how to defeat Cao Cao, he was told that Jiang Gan had come to see him. Zhou immediately figured out that Jiang must have come to persuade him to surrender. Zhou Yu devised a clever plan to thwart his efforts and enlisted the help of his subordinate to carry it out. Then he went to meet Jiang Gan all smiles. Zhou Yu took Jiang Gan's hands and marshaled him into his tent and treated him to a banquet. When all his generals and subordinates came for dinner, Zhou Yu told those around the table: "This is an old friend or mine. Though he came from the Cao Cao camp, he did not come to persuade me to surrender. Please do not suspect him."

After the banquet, Zhou Yu pretended that he had too much and invited Jiang Gan to his bedroom for a rest. Zhou Yu soon pretended to have fallen asleep. Jiang Gan took this chance to thumb through Zhou Yu's documents. He was shocked to find a letter from Cai Mao and Zhang Yun, two generals of the Cao camp, who had written Zhou Yu to surrender. Jiang hid letter of surrender in his pocket and returned to the bed, pretending that he was sill asleep.

After midnight, someone sneaked into Zhou Yu's tent and woke him up, telling him "A messenger came from the Cao camp to say that Cai Mao and Zhang Yun were not yet a position to carry out their plan." After he heard the news, Zhou Yu went back to sleep. Jiang Gan got up again silently and snuck out of Zhou Yu's camp. He crossed the river immediately and handed the letter of surrender to Cao Cao. Cao was enraged and he had Cai Mao and Zhang Yun executed.

When the news spread to Wu, Zhou Yu burst into laughter and said, "Cai Mao and Zhang Yun were the two generals I feared most. Now I fear no one." Before long, Cao cao realized that he was cheated by Zhou Yu's stratagem of sowing distrust in Cao's camp.