乐不思蜀 happy and carefree, without a thought for Shu
Explanation
这个成语的意思是：形容一个人在新的环境中非常快乐，以至于忘记了故乡，忘记了原来的生活。
This idiom describes someone who is so happy in a new environment that they forget their homeland and their old life.
Origin Story
三国时期，蜀国被魏国灭亡后，后主刘禅投降了魏国。魏国皇帝司马昭为了试探刘禅是否还怀念蜀国，特意为他举办了一场盛大的宴会，宴会上安排了蜀国歌舞表演。刘禅看得津津有味，毫无思念蜀国之意。司马昭问刘禅：“你难道不思念自己的故乡蜀国吗？”刘禅笑着说：“此间乐，不思蜀！”司马昭听后，不禁感叹刘禅真是个昏庸无能的君主。
During the Three Kingdoms period, the state of Shu was destroyed by Wei. The last emperor, Liu Chan, surrendered to Wei. To test Liu Chan's feelings for Shu, the Wei emperor, Sima Zhao, held a grand banquet for him, featuring Shu's dances and music. Liu Chan was captivated by the performance and showed no sign of missing Shu. Sima Zhao asked Liu Chan, "Don't you miss your homeland Shu?" Liu Chan smiled and said, "It's so pleasant here that I don't miss Shu!" Sima Zhao was taken aback and exclaimed that Liu Chan was indeed a weak and incompetent ruler.
Usage
这个成语可以用来形容一个人在新的环境中非常快乐，忘记了以前的烦恼。
This idiom can be used to describe someone who is so happy in a new environment that they forget their old troubles.
Examples
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他整天沉迷于游戏，乐不思蜀，忘记了学习的责任。
tā zhěng tiān chén mí yú yóu xì, lè bù sī shǔ, wàng jì le xué xí de zé rèn.
He is so addicted to video games that he forgets his responsibility to study.
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公司的新项目很有吸引力，大家都乐不思蜀，工作起来更有干劲。
gōng sī de xīn xiàng mù hěn yǒu xī yǐn lì, dà jiā dōu lè bù sī shǔ, gōng zuò qǐ lái gèng yǒu gàn jìn.
The company's new project is very attractive. Everyone is excited and working with more enthusiasm.
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在美丽的海岛上，我乐不思蜀，真想永远留在这里。
zài měi lì de hǎi dǎo shàng, wǒ lè bù sī shǔ, zhēn xiǎng yǒng yuǎn liú zài zhè lǐ.
On the beautiful island, I was completely captivated, and I wished to stay here forever.