九曲回肠 Nine twists of the intestines
Explanation
形容痛苦、忧虑、愁闷已经到了极点，形容心情变化起伏很大。
Describes the extreme point of pain, worry, and sadness, which means a mood changes greatly.
Origin Story
一位名叫李白的书生，从小就饱读诗书，梦想成为一位大诗人。他游历四方，见识了许多世事，心中充满了忧愁和烦恼。他写下了许多脍炙人口的诗篇，其中就有《梦游天姥吟留别》。这首诗描写了李白在梦中游览天姥山，看到了许多奇异的景象，最后回到了现实世界，心中感慨万千。诗中的“九曲回肠”就用来形容李白在梦中所经历的种种情感变化，以及他回到现实世界后的失落和惆怅。
A scholar named Li Bai, who had read widely since childhood, dreamed of becoming a great poet. He traveled far and wide, witnessing many things that filled him with sadness and worry. He wrote many popular poems, including "A Dream of the Heavenly姥 Mountain". This poem describes Li Bai's visit to Heavenly姥 Mountain in a dream, seeing many strange sights, and finally returning to the real world, with a lot of emotion. The phrase "nine twists of the intestines" in the poem is used to describe Li Bai's emotional changes in the dream and his loss and melancholy after returning to the real world.
Usage
多用于描写内心痛苦、忧愁达到极点的情景，也用来形容事物变化多端，难以捉摸。
It is often used to describe the scene where the inner pain and sorrow reach the peak, and also used to describe the multi-faceted and unpredictable things.
Examples
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这首歌的旋律让人久久回味，真是九曲回肠！
zhè shǒu gē de xián lǜ ràng rén jiǔ jiǔ huí wèi, zhēn shì jiǔ qū huí cháng!
The melody of this song is so memorable, it's really a 'nine twists of the intestines' experience!
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他为了梦想奋斗了这么多年，经历了无数的挫折，终于取得成功，这真是九曲回肠的传奇故事。
tā wèi mèng xiǎng fèn dòu le zhè me duō nián, jīng lì le wú shù de cuò zhí, zhōng yú qǔ dé chéng gōng, zhè zhēn shì jiǔ qū huí cháng de chuán qí gù shì.
He fought for his dream for so many years, experienced countless setbacks, and finally achieved success. This is really a legendary story of 'nine twists of the intestines'.