This idiom comes from an old Chinese fable.
A man loved to play the lute and was confident in his music.
One day, he sat down in front of a cow and played a beautiful melody.
The music was elegant and emotional, but the cow just kept chewing grass.
It didn’t react at all.
The man was confused — until he realized:
The cow couldn’t understand the music.
So he changed the tune.
This time, he played sounds like mosquitoes buzzing, cows mooing, and calves calling.
The cow finally stopped eating and listened carefully.
That became a metaphor:
If the listener can’t understand, even the best message won’t get through.