Zhao Kuo, son of the famed Zhao general Zhao She, devoured military texts as a boy and could debate tactics so skillfully that even his father was stumped. This made Zhao Kuo insufferably proud—he boasted that if he ever led an army, no one in the world could defeat him.
After King Zhao Huiwen of Zhao died, King Zhao Xiaocheng took power. The Qin army and the Zhao army confronted each other at Changping. By then, Zhao She had died, and the King of Zhao sent Lian Po to resist the Qin but failed, so he planned to replace Lian Po with Zhao Kuo. Senior Minister Lin Xiangru advised the King of Zhao, saying:
"Your Majesty, appointing Zhao Kuo as general because of his reputation for military strategy is like gluing the tuning pegs of a zither. Zhao Kuo has only memorized his father's military texts, but does not understand how to adapt them to actual circumstances."
The King of Zhao ignored all warnings and appointed Zhao Kuo as the general.
As a result, the Zhao army suffered a crushing defeat. After Zhao's 400,000 troops surrendered to Qin, they were all buried alive. Zhao Kuo himself was shot dead by Qin arrows during the battle.
"The 'se' is an ancient instrument; the 'zhu' is a short wooden peg used to adjust tuning. Gluing the tuning peg in place prevents movement. Later, the idiom 'gluing the peg to play the se' came to describe rigid stubbornness and inflexibility in handling matters."
Source: *Records of the Grand Historian*, "Biographies of Lian Po and Lin Xiangru"
Meaning of the Idiom: Later, the Chinese idiom "胶柱鼓瑟" came to describe rigid stubbornness and inflexibility in handling matters.