During the Spring and Autumn period, King Gong of Chu, whose primary wife had no sons, had to choose an heir from five sons born to other consorts: Prince Zhao, Zigàn, Zixi, Prince Wei, and Qiji. After much deliberation, he finally selected Prince Zhao as the crown prince.
In 560 BCE, King Gong of Chu died, and Crown Prince Zhao succeeded him, known historically as King Kang of Chu. After ruling for 15 years, King Kang fell ill and died, and his son Mi Jun took the throne. Mi Jun deeply trusted Prince Wei, appointing him as the prime minister, but the ambitious Prince Wei used his immense power to amass influence, secretly preparing to seize the throne for himself.
In 541 BCE, Prince Wei of Chu was on a diplomatic mission to the state of Zheng when, just as he reached the border, urgent news arrived that the King of Chu had fallen gravely ill. Overjoyed, he immediately whipped his horse into a gallop and raced back to the capital. Bursting into the palace, he assassinated the crown prince Mi Jun and declared himself king, later known in history as King Ling of Chu.
After ascending the throne, King Ling felt no one in the world could challenge him, so he entrusted military command to his most favored younger brother, Prince Qiji, and spent his days indulging in pleasure.
After Prince Qi Ji gained military command, he frequently led campaigns against neighboring small states, successively conquering Chen and Cai, steadily increasing his power and prestige. King Ling was pleased and granted him the land of Cai, appointing him Duke of Cai. But soon, the king grew uneasy about Qi Ji and summoned Grand Master Shen Wuyu, asking, "I have enfeoffed Qi Ji as Duke of Cai—what do you think of this?"
Shen Wuyu replied, "A ruler should not enfeoff close relatives outside the capital. Over time, their power will grow and threaten the state. As the saying goes: 'A branch too large will break; a tail too big cannot wag.' You must understand this principle."
Shen Wuyu's warning failed to rouse King Ling of Chu, who remained convinced that his most trusted younger brother, Qiji, would never betray him.
In 530 BCE, King Ling of Chu left his capital Ying with part of his army to go hunting in the countryside, and then launched an attack on the state of Xu, remaining away from home for an extended period.
Seeing that Chu's rear was undefended, a former minister of Cai urged Qi Ji to launch a surprise attack, and in one swift move they captured the capital. King Ling, realizing the tide had turned against him, hanged himself. Soon after, Qi Ji schemed to force Zi Gan and Zi Xi to their deaths, seized the throne, and became known to history as King Ping of Chu.
Later, people used the idiom "A Tail Too Big to Wag" to describe subordinates whose power becomes too great to control.
Source: *Zuo Zhuan*, "Duke Zhao's Eleventh Year"
Meaning of the Idiom: Later, the Chinese idiom "尾大不掉" came to describe how subordinates whose power becomes too great to control.