前功尽弃 previous efforts wasted
Explanation
指以前的功劳全部丢失，也指以前的努力全部白费。比喻事情快要成功的时候，却因为疏忽而失败，前功尽废。
Refers to the complete loss of previous merits or the waste of previous efforts. An idiom that describes how something fails just before success due to negligence, and all the previous work is wasted.
Origin Story
战国时期，秦国大将白起攻打魏国都城大梁，一位名叫苏厉的谋士前往周赧王进言，希望周王能够阻止秦军，他强调，如果大梁失守，周朝的安危将受到严重威胁。苏厉用楚国神箭手养由基的故事做比喻，养由基射箭技艺超群，百发百中，但如果最后一箭射失，那么之前的九十九箭都将白费。可惜周赧王并未采纳他的建议，最终大梁沦陷，周朝的命运也走向衰落。苏厉苦心劝谏，却因时机和决策失误而前功尽弃，留下千古叹息。
During the Warring States period in China, the Qin general Bai Qi planned to attack Da Liang, the capital city of the Wei state. A strategist named Su Li went to persuade King Nan of Zhou to prevent the Qin army's attack. He stressed that if Da Liang fell, the safety of the Zhou dynasty would be seriously threatened. Su Li used the story of the legendary archer Yang Youji as a metaphor: Yang Youji's archery skills were superb, never missing his mark, but if he missed his last arrow, all his previous ninety-nine arrows would be wasted. Unfortunately, King Nan of Zhou did not heed his advice, Da Liang fell, and the Zhou dynasty's fate also declined. Su Li's efforts to persuade the king were in vain, the timing and decisions were wrong, and his efforts were fruitless.
Usage
常用来形容事情因故失败，之前的努力付诸东流。
Often used to describe things that have failed for some reason, and the previous efforts are wasted.
Examples
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他辛辛苦苦准备了这么久，最后却因为一个小疏忽前功尽弃，真是令人惋惜！
ta xin xinku xinku zhunbei le zheme jiu, zuihou que yinwei yi ge xiao shuh pre gong jin qi, zhen shi ling ren wanxi
After so much hard work, he ended up losing it all because of a small oversight, what a pity!
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多年的努力付诸东流，前功尽弃，他感到无比的沮丧。
duonian de nuli fu zhu dongliu, qian gong jin qi, ta gandao wubi de jusang
Years of hard work were in vain, everything was lost, he felt incredibly depressed.