In 222 AD, Liu Bei of Shu Han launched a massive invasion of the Wu Kingdom, only to suffer a crushing defeat and flee in disgrace to Baidi City (present-day Fengjie County, Sichuan), where he died of illness the following year.
After Liu Bei's death, his 16-year-old son Liu Shan ascended the throne, known as the Later Ruler. Liu Shan was an incompetent and dim-witted ruler; initially, thanks to the guidance of Zhuge Liang and others entrusted by Liu Bei, the state was managed reasonably well. However, as these capable advisors passed away one after another, Liu Shan devoted himself solely to pleasure, causing the state's governance to deteriorate and its national strength to steadily weaken.
In 263 AD, Emperor Yuan of Wei ordered General Deng Ai, General Zhong Hui, and Governor Zhuge Xu to launch a three-pronged attack on Shu Han. The 56-year-old Liu Shan surrendered, becoming a prisoner of Wei, and Shu Han fell.
After the fall of Shu Han, Emperor Yuan of Wei ordered its last ruler, Liu Shan, to relocate to the Wei capital Luoyang. There, Liu Shan was granted the title Duke of Anle, along with a fief of ten thousand households, ten thousand servants, and noble titles for all his descendants. Content with these imperial gifts, the incompetent former emperor settled comfortably into a life of pleasure in a foreign land.
At that time, the man who truly held power in the Kingdom of Wei was General Sima Zhao. One day, he invited Liu Shan, the former ruler of Shu-Han, to a banquet and ordered performances of Shu-Han's local music and dances. The sight stirred deep sorrow in the hearts of the old Shu-Han officials present, and some even wept. Yet Liu Shan, the former sovereign, watched with great delight, laughing and enjoying himself as if he had never lost his kingdom.
After Sima Zhao noticed this situation, he quietly said to his trusted minister Jia Chong beside him:
“Unbelievable, a person could be so foolish! It seems that even if Zhuge Liang were alive, he couldn’t save his kingdom, let alone Jiang Wei!”
Jiang Wei was originally a general of Wei, but later surrendered to Shu and earned Zhuge Liang's trust. After Zhuge Liang's death, he became Grand General. When Liu Shan surrendered, Jiang Wei was forced to submit to Wei general Zhong Hui. The following year, Zhong Hui rebelled against Wei, pretending to ally with Jiang Wei in a plot to restore Shu Han, but the scheme failed and both were killed.
A few days later, Sima Zhao directly asked Liu Shan, "Do you still miss Shu?" Liu Shan shook his head and said, "I'm extremely happy here; I don't miss Shu at all."
When Xi Zheng, who had previously served as a secretary in Shu, learned of this, he quickly advised Liu Shan privately: "If Sima Zhao asks again whether you miss Shu, you should weep and reply: 'My ancestors' tombs are far away in Shu; there is not a day I do not long for them!' That way, you may still hope to return to Shu."
A few days later, Sima Zhao indeed asked Liu Shan again if he still missed Shu. Following Xi Zheng's instructions, Liu Shan recited the prepared reply and even forced out a few tears.
Unexpectedly, Sima Zhao already knew that Xi Zheng had taught Liu Chan to say this. After hearing Liu Chan's reply, he laughed heartily and said, "These are Xi Zheng's words! How is it that what you said matches his exactly? I suppose he taught you to say this, didn't he?"
Liu Shan said nervously, "Yes, it is exactly as you think."
Those nearby could not help but burst into laughter upon hearing this.
Later, people derived the idiom "So Happy He Forgot His Homeland" from this history, meaning to enjoy oneself so much that one forgets to return or forgets one's roots.
Source: *Records of the Three Kingdoms*, "Biography of Liu Shan, the Later Ruler"
Meaning of the Idiom: Later, the Chinese idiom "乐不思蜀" came to describe enjoy oneself so much that one forgets to return or forgets one's roots.