得鱼忘筌 Get the fish, forget the trap
Explanation
比喻达到目的后，便忘记了凭借的东西。也比喻只顾眼前利益，忘记根本。
The idiom is used to describe someone who forgets the means by which they achieve their goal. It also refers to someone who only focuses on short-term gains and forgets the fundamental principles.
Origin Story
很久以前，有个老渔夫，他很擅长捕鱼。他用竹编的筌（quán）在河里捕鱼，筌是一个漏水的竹器，鱼很容易进去，却很难出来。有一天，他用筌捕到了一条又肥又大的鱼。他高兴极了，抓起鱼就走，把筌扔在了河边。回家后，妻子问他怎么没把筌带回来，老渔夫才想起来，只顾着高兴得鱼了，把工具都忘了。这个故事告诉我们，做事不能只顾眼前利益，要懂得感恩，不能得鱼忘筌。
Long ago, there was an old fisherman who was very good at fishing. He used a bamboo trap called a 'quan' to catch fish in the river. The quan was a leaky bamboo contraption; fish could easily get in, but it was difficult for them to get out. One day, he caught a large, fat fish with the quan. He was overjoyed, grabbed the fish, and left, forgetting the quan on the riverbank. When he got home, his wife asked him why he hadn't brought the quan back. Only then did the old fisherman remember that he was so happy about catching the fish that he had forgotten his tool. This story tells us that we shouldn't only care about immediate benefits; we should be grateful and not forget the means by which we achieve our goals.
Usage
常用作比喻，形容只顾眼前利益，忘记根本。
Often used as a metaphor to describe someone who focuses only on short-term gains and forgets fundamental principles.
Examples
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他为了升官发财，不择手段，真是得鱼忘筌，最终落得个身败名裂的下场。
tā wèile shēngguān fācái, bùzé shǒuduàn, zhēnshi dé yú wàng quán, zuìzhōng luò de gè shēn bài míngliè de xiàchǎng.
He used every means to get promoted and rich, truly forgetting the means for the end. In the end, he lost everything.
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取得成功后，他忘记了曾经帮助过他的人，真是得鱼忘筌啊！
qǔdé chénggōng hòu, tā wàngjìle céngjīng bāngzhù guò tā de rén, zhēnshi dé yú wàng quán a！
After achieving success, he forgot those who had helped him; it was a case of 'getting the fish and forgetting the trap'.