Zhu Gejin, styled Ziyu, was the elder brother of Zhuge Liang, the famed chancellor of Shu Han during the Three Kingdoms period. Serving in Eastern Wu, he was highly valued by its ruler Sun Quan and rose to the rank of Grand General.
Zhuge Jin was extremely loyal to Sun Quan. Once, Sun Quan tried to send him to recruit Zhuge Liang, but he replied, "Liang will not come, just as Jin will not go." Sun Quan greatly appreciated this.
Zhuge Jin's son, Zhuge Ke, was exceptionally clever and sharp-tongued from a young age, which made Sun Quan quite fond of him.
When Zhuge Ke was six, he once attended a court banquet with his father. Zhuge Jin had a long face like a donkey, so Sun Quan, in high spirits from wine, decided to tease him. He ordered a donkey brought in and had the words "Zhuge Ziyu" written on its long face. Everyone burst into laughter, and Zhuge Jin was deeply embarrassed.
Zhuge Ke saw this and felt indignant for his father. After a moment's thought, he approached Sun Quan, knelt, and requested permission to add two characters to the donkey's name. Sun Quan, intrigued, ordered someone to hand Zhuge Ke a brush. Zhuge Ke then added "zhi lü" (meaning "the donkey") after "Zhuge Ziyu."
The donkey was thus dubbed "Zhuge Ziyu's Donkey," and everyone present praised Zhuge Ke's clever wit. Emperor Sun Quan, delighted, immediately gifted the donkey to Zhuge Ke. On another occasion, Sun Quan asked Zhuge Ke, "Tell me, who is more accomplished—your father or your uncle Zhuge Liang?" "My father," Zhuge Ke replied. When pressed for a reason, he explained, "My father knows how to serve a wise ruler, but my uncle does not. That is why my father is superior." Sun Quan, greatly pleased, praised him lavishly and said to Zhuge Jin, "They say Lantian produces fine jade, and a general's gate breeds a tiger cub—truly, this is no empty saying." Lantian was a region famous for its jade, and Sun Quan used the metaphor to honor Zhuge Jin for having a son as precious as jade. Thus, the idiom "Lantian Produces Jade" came to mean that a distinguished family gives rise to worthy offspring.
Source: *Records of the Three Kingdoms*, "Biography of Zhuge Ke"
Meaning of the Idiom: Later, the Chinese idiom "蓝田生玉" came to describe a distinguished family gives rise to worthy offspring.