千载难逢 once in a thousand years
Explanation
千载难逢的意思是一千年也难碰到一次，形容机会极其难得。
千载难逢 means it is once in a thousand years, describing how rare and valuable an opportunity is.
Origin Story
传说，在古代，有一位名叫王羲之的书法家，他以精妙的书法闻名天下。有一天，他正在家中练字，突然听到有人敲门。开门一看，原来是一位名叫谢安的官员，谢安是当时有名的政治家，他此次来拜访王羲之，是希望王羲之能为他的书法作品题字。王羲之非常高兴，因为他知道谢安是自己的仰慕者，而且谢安的书法也非常好，所以他欣然答应了。王羲之提笔写下了一段精妙的文字，谢安看后赞叹不已，连连称奇。他告诉王羲之：“你这样的书法，真是千载难逢，世上难觅其二！”王羲之谦虚地说：“过奖了，我只是尽力而为而已。”从此，王羲之的书法名声更加远播，他的作品也成为后世书法家的学习典范。
Legend has it that in ancient times, there was a calligrapher named Wang Xizhi who was known throughout the world for his exquisite calligraphy. One day, he was practicing calligraphy at home when he suddenly heard a knock on the door. He opened the door and saw an official named Xie An. Xie An was a famous politician of the time, and he had come to visit Wang Xizhi, hoping that Wang Xizhi would inscribe his calligraphy works. Wang Xizhi was very happy because he knew that Xie An was his admirer, and Xie An's calligraphy was also very good, so he readily agreed. Wang Xizhi picked up his pen and wrote a piece of exquisite writing. Xie An was amazed and praised it endlessly. He told Wang Xizhi:
Usage
这个成语形容机会极其难得，可以用于表达对机会的珍惜和重视。
This idiom describes how rare and valuable an opportunity is. It can be used to express how much one cherishes and values an opportunity.
Examples
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这次的机会是千载难逢，我们一定要把握住。
ci ci de ji hui shi qian zai nan feng, wo men yi ding yao ba wo zhu.
This is a once-in-a-lifetime opportunity, we must seize it.
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他终于等到了千载难逢的机会，决定去创业。
ta zhong yu deng dao le qian zai nan feng de ji hui, jue ding qu chuang ye.
He finally waited for a once-in-a-lifetime opportunity and decided to start a business.
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这样的良机可谓是千载难逢，不容错过。
zhe yang de liang ji ke wei shi qian zai nan feng, bu rong cuo guo.
Such a good opportunity is a once-in-a-lifetime opportunity, don't miss it.