This idiom means wasting effort on the wrong audience.
Gǔ shíhou yǒu gè yīnyuèjiā jiào Gōngmíng Yí
古时候Gǔ shíhou🔊，有个yǒu gè🔊音乐家yīnyuèjiā🔊叫jiào🔊公明仪Gōngmíng Yí🔊。
Tā duì yì tóu niú tánqín qínshēng fēicháng yōuměi
他tā🔊对duì🔊一头yì tóu🔊牛niú🔊弹琴tánqín🔊，琴声qínshēng🔊非常fēicháng🔊优美yōuměi🔊。
Kěshì niú gēnběn bù lǐ zhǐgù chī cǎo
可是Kěshì🔊牛niú🔊根本gēnběn🔊不理bù lǐ🔊，只顾zhǐgù🔊吃草chī cǎo🔊。
Gōngmíng Yí míngbai le duì bù dǒng yīnyuè de rén tánqín shì báifèi lìqì
公明仪Gōngmíng Yí🔊明白了míngbai le🔊，对duì🔊不懂bù dǒng🔊音乐yīnyuè🔊的de🔊人rén🔊弹琴tánqín🔊是shì🔊白费báifèi🔊力气lìqì🔊。
English Translation:
In ancient times, there was a musician named Gongming Yi. He played the lute to a cow, and the music was very beautiful. But the cow completely ignored it and just kept eating grass. Gongming Yi understood that playing the lute to someone who doesn't understand music is a waste of effort.