During the Spring and Autumn period, as the Eastern Zhou dynasty weakened, various feudal states sought to swallow their rivals and seize the throne.
In 655 BCE, the powerful state of Jin, one of the five hegemons, plotted to annex its smaller neighbors, Yu and Guo, to expand its territory. The Jin ruler pondered, "If we attack Guo first, our army must pass through Yu. If Yu blocks us or joins Guo, we'll face two enemies at once." His advisor Xun Xi proposed a cunning plan: "Let's bribe the Yu ruler with our finest jade and horses. He's greedy and will surely let us pass." The Jin ruler hesitated, "But those are my treasures!" Xun Xi replied, "Think of it as temporarily storing them in Yu's treasury. Once we conquer Guo, Yu will be defenseless, and we'll get them back." The plan worked—the Yu ruler accepted the bribes and allowed Jin troops through, ignoring his minister Gong Zhiqi's warning: "A lip without teeth is cold; Guo is our shield!" Jin crushed Guo, then on the return, ambushed Yu, reclaiming the treasures. This story gave rise to the idiom "Borrowing a Path to Destroy Guo," a classic lesson in short-sighted greed.
Jin official Xun Xi advised Duke Xian of Jin, "Duke Yu is greedy. If we gift him the thousand-li horse from Qu and the fine jade from Chuiji, asking to borrow his road for our troops, I believe he will agree."
Duke Xian of Jin said, "This thousand-li horse and fine jade are treasures of our Jin state—how can we casually give them away?" Xun Xi smiled, "Your Majesty, this is merely a temporary deposit in the state of Yu, just like keeping them in our own home!"
Duke Xian of Jin understood Xun Xi's plan, so he sent Xun Xi with fine horses and precious jade to visit Duke Yu of Yu.
Upon hearing the news, Gong Zhiqi, a senior official of the Yu State, immediately went to advise Duke Yu, saying, "The cheeks and the jawbone depend on each other; without the lips, the teeth would feel the cold. The relationship between the Guo and Yu states is exactly like that of lips and teeth, so we absolutely must not 'lend a path' to the Jin army!"
Duke Yu, short-sighted and greedy, ignored Gong Zhiqi's wise advice, saying, "Jin and Yu share the same ancestor—how could they harm us? Refusing them passage would be too unfriendly..."
Thereupon, Duke Yu of Yu accepted the gifts with delight and agreed to Jin's request to "borrow a road." Gong Zhiqi foresaw that Yu would be doomed beyond saving, so he took his entire family and fled early to the State of Cao.
With Duke Yu's "generous assistance," Jin smoothly annihilated Guo. On the return, under the pretext of resting troops, they camped in Yu. Catching Yu completely off guard, they launched a surprise attack and swiftly conquered Yu. Duke Yu was captured, while the famed horses and fine jade returned to Duke Xian of Jin's hands.
Later, the idiom "Without the lips, the teeth grow cold" came to describe a close relationship where one's interests are tied to another's.
Source: *Zuo Zhuan*, "Duke Xi's Fifth Year"
Meaning of the Idiom: Later, the Chinese idiom "唇亡齿寒" came to describe how a close relationship where one's interests are tied to another's.