During the late Eastern Han Dynasty, the Wu Kingdom's commander-in-chief was the famed general Zhou Yu, styled Gongjin, a native of Shu County in Lujiang (present-day Shucheng, Anhui). The people of Wu affectionately called him "Young Master Zhou." Born into a scholar-official family, he was close friends with Sun Ce and helped him establish the Sun-Wu regime. After Sun Ce's death, Zhou Yu and Zhang Zhao jointly assisted Sun Quan in governing. In 208 AD, when Cao Cao led his army south, Zhou Yu and Lu Su firmly advocated resistance, personally commanding Wu forces to a great victory over Cao's troops at Red Cliffs. Two years later, Zhou Yu fell ill and died at the young age of thirty-five.
Zhou Yu was not only a brilliant strategist and military commander, known for his resourcefulness, but also a master of music with an extraordinary ear. Even after several cups of wine, when slightly tipsy, he could detect the slightest mistake in any performance. Whenever he caught an error, he would simply glance at the musician to signal the flaw. A popular rhyme of the time said, "If the tune goes wrong, Zhou Yu will look."
Tang Dynasty poet Li Duan wrote in his poem "Listening to the Zither": "To win a glance from Zhou Lang, I often purposely pluck the wrong string." Later, the idiom "Zhou Lang's Critique" came to refer to a music critic or connoisseur.
Source: *Records of the Three Kingdoms*, "Biography of Zhou Yu"
Meaning of the Idiom: Later, the Chinese idiom "顾曲周郎" came to describe a music critic or connoisseur.