以貌取人 — “To judge a person by their outward appearance”

The idiom '以貌取人' (yǐ mào qǔ rén) originates from an anecdote involving Confucius and his disciples, as recorded in 'Records of the Grand Historian: Biographies of Confucius's Disciples.' Confucius had numerous students, among whom was Zai Yu, who was initially eloquent and persuasive, leaving a good impression on the master. However, Zai Yu later revealed his true nature: he lacked virtue and was extremely lazy, even sleeping during study hours in broad daylight. Confucius was disappointed and famously remarked that he was 'rotten wood that cannot be carved.'

Another disciple was Tantai Mieming, whose courtesy name was Ziyu. He was from the State of Lu and was thirty-nine years younger than Confucius. Ziyu had a rather unattractive physical appearance, and Confucius initially believed he was of low aptitude and would not achieve much.

However, after becoming a student, Ziyu dedicated himself to self-cultivation and practiced righteous conduct. He always acted honorably and avoided improper paths, only meeting high officials for public affairs. Later, Ziyu traveled to the Yangtze River region, attracting over three hundred disciples, and his reputation spread widely among various states.

When Confucius heard of Ziyu's success, he deeply reflected on his initial judgments. He lamented, 'I used to judge people by their words, and I was wrong about Zai Yu. I used to judge people by their appearance, and I was wrong about Ziyu.' This story teaches us not to make superficial judgments based solely on outward appearances or initial impressions, but rather to look for inner qualities and true abilities.