Literal meaning

facing (对) — ox (牛) — pluck (弹) — qin (琴)

Origin

Han-dynasty work Like Tone (《理惑论》) by Mou Rong. A musician played a beautiful melody to a grazing cow; the cow kept its head down, indifferent. He then mimicked a mosquito's buzz and a calf's cry — and the cow lifted its head and listened. The lesson Mou Rong drew: communication only lands when the audience is attuned to what's being said. The phrase has been used since to describe the futility of explaining things to someone who can't (or won't) understand.

Examples

Usage & nuances

Often self-deprecating ("I was casting pearls before swine"). Mildly insulting to the listener if used in their hearing — comes across as rude if overheard.