[刘禅, Liú Shàn] is so content that he does not think of 蜀 (Shǔ). See story.
To be so content that you don't think about returning to your roots or where you came from
Negative
久在北京的他有点乐不思蜀了 | Jiǔ zài běijīng de tā yǒudiǎn lèbùsīshǔ le
After a long time in Beijing, he kind of forgot about where he came from
[Source]
你到了外国，可不能乐不思蜀，忘记养育你的故乡故土啊 | Nǐ dào le wàiguó, kě bùnéng lèbùsīshǔ, wàngjì yǎngyù nǐ de gùxiāng gùtǔ a
After you go abroad, you can't have such a good time that you forget about your home
[Source]
None
None
None
《三国志》(Sān Guó Zhì) by 陈寿 (Chén Shòu). The historical text covers the events of the end of the Eastern Hàn Dynasty (东汉, Dōng Hàn, 25 - 220) and the Three Kingdoms period (220 - 280)
Near the end of the Three Kingdoms Period (三国时期, 220 - 280 BC), the kingdom of 魏 (wèi) conquered the kingdom of 蜀 (shǔ). The emperor of 蜀, 刘禅 (Liú Shàn), was taken back to the 魏 capital as a prisoner. However, instead of being killed, he was given a title and a place to live out the rest of his days, and he resumed the life of pleasure that he'd maintained back home.
One day, 刘禅's captors arranged for a feast. At the feast, in attempts to humiliate the former emperor, they had performers perform dances from the now-dead country of 蜀. Instead of being saddened by evidence of what he had lost, however, 刘禅 was delighted. Seeing this reaction, his bewildered captors asked the former emperor whether he missed his home. 刘禅 replied that he was so content that he wasn't even thinking of home.