A metaphor for two closely interdependent entities, where the downfall or weakening of one will inevitably affect or endanger the other.
Era:
Ancient
Frequency:
Story:
During the Spring and Autumn period, Duke Xian of Jin wanted to expand his power and territory. He found an excuse, claiming that the neighboring State of Guo frequently encroached upon Jin's borders, and decided to dispatch troops to conquer Guo. However, the State of Yu lay between Jin and Guo, and attacking Guo required passage through Yu's territory. 'How can we successfully pass through Yu?' Duke Xian asked his ministers.
Minister Xun Xi replied, 'The ruler of Yu is shortsighted and covetous of petty gains. If we present him with priceless jade and precious horses, he will not refuse to grant us passage.' Duke Xian was a little reluctant at first. Xun Xi, perceiving the Duke's thoughts, said, 'Yu and Guo are neighbors, interdependent like lips and teeth. If Guo is destroyed, Yu cannot survive alone. Your jade and horses will merely be temporarily stored with the Duke of Yu.' Duke Xian adopted Xun Xi's strategy.
Upon seeing the two valuable gifts, the ruler of Yu was overjoyed. When Xun Xi mentioned the request to borrow passage through Yu, he immediately agreed without hesitation. Gong Zhiqi, a minister of Yu, heard about this and quickly tried to stop him, saying, 'No, no! Yu and Guo are neighbors, interdependent like lips and teeth. Our two small states rely on each other and can help each other in times of need. If Guo is destroyed, our State of Yu will also be difficult to preserve. As the saying goes, "If the lips are gone, the teeth will be cold" – without lips, the teeth cannot be protected! Granting passage to Jin is absolutely impermissible.'
The Duke of Yu said, 'Jin is a powerful state, and now they are specially sending us precious jade and horses to befriend us. Are we not even allowed to let them pass through our territory?' Gong Zhiqi sighed repeatedly, knowing that the day of Yu's downfall was not far off, so he took his entire family and left the State of Yu.
As expected, the Jin army, having passed through Yu, destroyed Guo. Afterwards, they seized the Duke of Yu, who had personally welcomed the Jin army, and conquered Yu.