对牛鼓簧 playing to the cows
Explanation
比喻对不了解道理的人讲道理，或对愚蠢的人说话，意思是白费力气。
A metaphor used to describe trying to reason with someone who doesn't understand reason, or speaking to a foolish person, meaning it's a waste of effort.
Origin Story
从前，有一个秀才，他学富五车，满腹经纶，可是他却恃才傲物，目中无人。一天，他去乡下探望一位朋友，朋友家养了一头老牛，这只老牛非常温顺老实，从不惹是生非。秀才看到这只老牛，便想试试自己的口才，于是就走到老牛跟前，滔滔不绝地讲起了大道理，他讲了孔孟之道，讲了治国安邦的大计，还讲了人生的意义和价值。他讲得口干舌燥，满头大汗，可是老牛却只是默默地吃草，对他的话根本听不进去。最后，秀才讲完了，累得瘫坐在地上，他这才明白，自己对牛鼓簧，是多么的愚蠢。他自嘲地笑了笑，起身告辞了。
Once upon a time, there was a scholar who was very learned and knowledgeable, but he was arrogant and looked down on others. One day, he went to the countryside to visit a friend. His friend kept an old ox, which was very docile and honest, and never caused trouble. When the scholar saw the ox, he wanted to test his eloquence, so he walked up to the ox and began to talk endlessly about great truths. He talked about the Way of Confucius and Mencius, about the great plan of governing and stabilizing the country, and also about the meaning and value of life. He spoke until he was hoarse and sweating profusely, but the ox just silently ate grass, not listening to his words at all. Finally, the scholar finished speaking and collapsed to the ground, exhausted. Only then did he realize how foolish it had been to speak to the ox. He smiled self-deprecatingly, got up, and took his leave.
Usage
常用来形容对愚笨的人讲道理，或对不懂的人解释事情，结果是徒劳无功的。
Often used to describe trying to reason with a foolish person, or explaining something to someone who doesn't understand, resulting in futile effort.
Examples
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他对那些不懂装懂的人，总是无可奈何地摇摇头，觉得简直是‘对牛弹琴’。
tā duì nàxiē bù dǒng zhuāng dǒng de rén, zǒng shì wú kě nài hé de yáo yáo tóu, jué de jiǎnzhí shì ‘duì niú tán qín’。
He would always shake his head helplessly at those who pretended to understand but didn't, and felt that it was simply "playing to the cows".
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在这次会议上，他提出的方案，对于一些经验丰富的管理人员来说，简直就是‘对牛鼓簧’。
zài zhè cì huì yì shàng, tā tí chū de fāng'àn, duì yú yīxiē jīngyàn fēngfù de guǎnlǐ rényuán lái shuō, jiǎnzhí shì ‘duì niú gǔ huáng’。
At this meeting, his proposed plan was simply "playing to the cows" for some experienced managers.