不由自主 involuntarily
Explanation
指由不得自己，控制不住自己。表示某种行为或情绪不受自己意志的支配。
It means that one cannot help oneself, cannot control oneself. It indicates that a certain behavior or emotion is not subject to one's own will.
Origin Story
话说很久以前，在一个偏远的山村里，住着一位名叫阿美的年轻女子。阿美心地善良，勤劳能干，深受乡亲们的喜爱。然而，她却有一个奇怪的毛病，每当夜深人静的时候，她就会不由自主地开始唱歌，歌声清脆婉转，但却带着一丝忧伤，仿佛在诉说着一段不为人知的往事。村民们对此感到非常好奇，但却没有人敢去询问她，只当她是被某种神秘的力量所控制着。 有一天，一位云游四方的道士来到了这个村子，听说阿美的情况后，便主动找到了她。道士仔细观察了阿美的状况，发现她并非被邪魔附体，而是因为心中压抑着一股悲伤的情绪，无法释放，所以才会不由自主地唱歌。道士向阿美讲述了因果轮回的道理，并教给她一些调节情绪的方法。 在道士的帮助下，阿美逐渐解开了心结，那股压抑已久的情绪也随之释放。从此以后，她不再不由自主地唱歌，而是过上了平静幸福的生活。她那清脆婉转的歌声，也只在欢乐的节日里才会响起。
Once upon a time, in a remote village, there lived a young woman named Amy. Amy was kind-hearted, hardworking, and loved by the villagers. However, she had a strange habit: every night, when it was quiet, she would involuntarily start singing. Her singing was clear and melodious, but with a touch of sadness, as if telling an untold story. The villagers were very curious, but no one dared to ask her, thinking she was controlled by some mysterious force. One day, a Taoist priest who traveled the world came to the village. Upon hearing about Amy's condition, he sought her out. The Taoist carefully observed Amy's condition and found that she was not possessed by evil spirits, but that she had suppressed sadness inside her that she couldn't release, so she would sing involuntarily. The Taoist told Amy about the principles of karma and reincarnation, and taught her some ways to regulate her emotions. With the Taoist's help, Amy gradually resolved her inner conflicts, and the long-suppressed emotions were released. From that day on, she no longer sang involuntarily, but lived a peaceful and happy life. Her clear and melodious singing only sounded on joyous festivals.
Usage
常用来形容人的行为或情绪不受自己控制。
It is often used to describe a person's behavior or emotions that are beyond their control.
Examples
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他吓得脸色发白，不由自主地颤抖起来。
tā xià de liǎnsè fābái, bù yóu zì zhǔ de chàndǒu qǐlái.
He turned pale with fright, and involuntarily trembled.
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面对突如其来的灾难，人们不由自主地流下了眼泪。
miàn duì tú rú qǐ lái de zāinàn, rénmen bù yóu zì zhǔ de liúlèi le yǎnlèi.
Faced with the sudden disaster, people involuntarily shed tears.
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听到这个好消息，他不由自主地笑了。
tīng dào zhège hǎo xiāoxi, tā bù yóu zì zhǔ de xiàole
Hearing the good news, he involuntarily smiled.