When the state of Jin planned to conquer Guo, it needed to pass through the state of Yu. A minister of Yu warned his lord: "Jawbone and cheek depend on each other. When the lips are gone, the teeth feel cold. If Guo falls, Yu will be next."
The lord of Yu accepted Jin's gifts and allowed passage. Jin conquered Guo — and on the way back, conquered Yu as well.
"唇亡齿寒" (when the lips are gone, the teeth feel cold) became the Chinese idiom for the interdependence of allies — and the fatal mistake of abandoning them.
辅车相依，唇亡齿寒。
辅车相依，唇亡齿寒。
Reflection & Analysis · 寓意解读
Core Wisdom
The neighbor you betray today is the buffer that protects you tomorrow. When the shield falls, the sword reaches you.
This story from the Zuozhuan is one of the most cited strategic parables in Chinese history. The lord of Yu's error was not stupidity — it was greed. He saw Jin's gifts and ignored the structural reality: Yu and Guo were interdependent. By allowing Guo to fall, Yu destroyed its own defense.
The idiom applies to any situation where short-term gain blinds someone to long-term strategic reality: a company that destroys a supplier, a country that abandons an ally, a person who betrays a friend for temporary advantage.