This idiom comes from Records of Three Kingdoms·Kingdom of Shu·Biography of the Last Emperor． In 223 AD，the founder of the Sun of the Three Kingdoms Period，Liu Bei was dead． His son，sixteen years old，Liu Shan succeeded the throne and was known as the Last Emperor. At first， under the assistance of the great prime minister Zhuge Liang，the young ruler managed his country with an effort. But after Zhuge Liang died， he wasmuddleheadedandincompetent，doingnothing everyday. Later the Kingdom of Shu was subjected by the Kingdom of Wei in 263 AD， Liu Shan surrendered and with some of his aids， were resettled in Luoyang， the capital of the Kingdom of Wei.The emperor of Wei granted his title as Duke Anle， Liu was very satisfied with this and still enjoyed his happy life there.

One day the Duke of Wei， Sima Zhao gave a banquet in honour of Liu Shan and arranged to have music and dance from Shu by some beautiful girls as the entertainment. The performance made Liu's aids very sad and homesick. But only Liu Shan looked very happy without any sorrow of national subjection. When Sima Zhao asked him: \"Don't you miss your hometown of Shu？\" He answered: \"How happy I am here! I think no more of Shu.\" From this story comes the idiom \"Le Bu Si Shu\"--so happy as to forget home and duty.

Now we use it to describe that one indulges in pleasure and forgets his home or his past suffering.

此語出自《三國志·蜀志·后主傳》。公元223年，三國時期蜀漢的創(chuàng)立者劉備病逝，他十六歲的兒子劉禪即位，稱后主。剛即位時，在諸葛亮等人的輔佐下，尚能治理國家。諸葛亮等先后去世后，劉禪便昏庸無能，只知玩樂，終于在公元263年被魏國滅亡，劉禪投降成了俘虜。魏帝曹奐讓劉禪到魏國都城洛陽居住，并封他為安樂公。劉禪對此非常知足，在異鄉(xiāng)過著享樂生活。

有一天，掌握魏國大權的晉王司馬昭宴請劉禪，席間為他專門表演了蜀地歌舞。在場的蜀漢舊臣看了都十分悲傷，只有劉禪喜笑自若，全無亡國之恨。席間，司馬昭問他：“頗思蜀否？”劉禪很快回答：“此間樂，不思蜀?！庇纱说贸龃说洹皹凡凰际瘛薄?/p>

后用此典比喻某人只知在外尋歡，樂而忘返，也用以表示樂而忘本。