Di Renjie, a renowned Tang Dynasty official from Taiyuan in Bingzhou, showed remarkable composure even as a child. One day, a guest was murdered, and officials came to interrogate the household. Everyone rushed to defend themselves, but Di Renjie remained seated, reading aloud. Annoyed, an official approached and scolded him. Di Renjie replied, "I am conversing with the sages in these books—when would I have time to talk to a petty clerk like you?"
When Di Renjie first became an official, serving as a military advisor in Bianzhou, he was falsely accused of a crime. The imperial inspector Yan Liben interrogated him and, recognizing Renjie's extraordinary talent, blurted out in praise, "Confucius said that by observing a person's mistakes, you can know their character—you, sir, are truly a pearl overlooked by the sea." He then recommended Renjie for the position of legal advisor in Bingzhou.
A colleague, Zheng Chongzhi, was assigned to travel to a very distant place, but his mother was elderly and ill. Di Renjie asked the chief secretary, Lin Renji, to allow him to go in Zheng's place. Lin Renji then praised Renjie's virtue to everyone, saying, "A man as virtuous as Duke Di is the only one south of the Big Dipper."
"Canghai Yizhu" (Pearl Left in the Sea): A pearl lost in the vast ocean. Later used to describe overlooked talent or hidden treasure.
Source: *New Book of Tang*, "Biography of Di Renjie"
Meaning of the Idiom: Later, the Chinese idiom "沧海遗珠" came to describe overlooked talent or hidden treasure.