During the Spring and Autumn period, Duke Huan of Qi led a coalition of feudal armies to invade the state of Cai. Yet, unsatisfied, he pressed on, determined to attack the state of Chu as well.
At the time, the State of Chu lay far to the south while Qi was in the north, an immense distance apart. All of Duke Huan of Qi's ministers urged him not to act rashly, but his ambition had swelled beyond reason, and he refused to heed any advice, stubbornly insisting on attacking Chu.
The state of Chu was gripped by panic, its people living in constant fear of a sudden invasion from Qi.
King Cheng of Chu was beside himself with anxiety, the state teetering on the brink of crisis. He thought, "I must find a way to calm the people and restore the peace we once knew!"
At this moment, a brave minister of Chu stepped forward and said to King Cheng of Chu, "Your Majesty, I am willing to go as an envoy to the Qi army camp."
King Cheng of Chu then dispatched him as an envoy to the Qi military camp to deliver his persuasive arguments.
Upon meeting King Huan of Qi, he said, "Your Majesty, your people of Qi dwell in the north, while our Chu lies in the south, thousands of li apart. If your horses or cattle were to stray, could they ever wander into our territory?"
"How is that possible?" Duke Huan of Qi dismissed it with a laugh.
The Chu envoy declared with righteous indignation, "Our kingdom was at peace, our people industrious and joyful—yet now your armies threaten to trample our lands, leaving our citizens in constant fear and our court deeply aggrieved. Why is this? Has Chu provoked you? If you refuse to withdraw, all of Chu will rise up and fight to the last!"
Duke Huan of Qi was left speechless and immediately withdrew his troops.
Later, people used the idiom "as unrelated as wind, horse, and cow" to describe things that have absolutely nothing to do with each other.
Source: *Zuo Zhuan*, Chapter "Duke Xi's Fourth Year"
Meaning of the Idiom: Later, the Chinese idiom "风马牛不相及" came to describe how things have absolutely nothing to do with each other.