多行不义必自毙 — “He who commits many unjust deeds is sure to bring about his own ruin”

During the Spring and Autumn Period, Duke Wu of Zheng had two sons, Zhuang Gong and Gong Shu Duan. After Duke Wu's death, his eldest son, Duke Zhuang, succeeded him.

However, Zhuang Gong's younger brother, Gong Shu Duan, with the strong support of their mother, Lady Jiang, vigorously expanded his fiefdom and actively prepared to usurp the throne.

Upon learning this, Duke Zhuang's minister, Ji Zhong, earnestly advised Duke Zhuang, saying, "Your Majesty, you must take action soon! Gong Shu Duan's power has grown significantly. If this continues, he will surely seize your throne!" Duke Zhuang, however, replied, "He who commits many unjust deeds is sure to bring about his own ruin. Just wait and see!"

As expected, Gong Shu Duan's influence continued to grow, bringing the western and northern borders of Zheng under his control, extending all the way to Lin Yan. At the same time, he relentlessly built fortifications, accumulated provisions, and gathered troops. He also arranged for his mother, Lady Jiang, to conspire from within, planning to attack and capture the capital of Zheng.

Duke Zhuang had long been prepared. Seizing the opportunity when Gong Shu Duan advanced towards the capital, he launched a surprise attack on Gong Shu Duan's base. The farmers, who had long suffered under Gong Shu Duan's oppression, also joined the battle, causing Gong Shu Duan's army to be defeated. He fled to another location, but Duke Zhuang's army pursued him.

Finally, with no escape route, Gong Shu Duan was forced to commit suicide.