对牛弹琴

In ancient time, there lived a musician named Gong Mingyi. He was very good at playing the Zheng, a plucked string instrument. But he also behaved foolishly sometimes. 

One day, he saw a cow eating grass in the field near his house. He was inspired by the scene and ran outside to play a tune for the cow. Gong Mingyi played beautifully and he himself was intoxicated（喝醉的） by the music. But the cow paid no heed to（不注意） the elegant sounds. It simply focused its attention on eating the grass. Gong Mingyi was surprised to see that. He couldn't understand why the cow was so indifferent to his performance. Obviously, it is not because his performance is poor. But the cow neither understood nor appreciated his elegant music!

From that story comes the idiom "Play the lute to a cow", which implies that someone speaks or writes without considering his audience. In general speaking, the speaker or writer has over-estimated his listeners or readers. In these cases, the idiom mocks the audience rather than the speaker.