Lips and Teeth 唇亡齿寒

The Chinese idiom 唇亡齿寒 (chun2 wang2 chi3 han2) literally means if there are no lips the teeth feel cold and comes from a story about a bloody battle during the Spring and Autumn Period (770-476 BC).

Duke Jinxian of the State of Jin wanted to annex the neighbouring State of Guo. One of the Duke's advisers suggested that the most likely way to succeed was to launch a surprise attack from the State Yu, also a neighbour of Guo. In fact, the adviser suggested that this approach would kill two birds with one stone because the Jin troops could not only crush the State of Guo, but they could also seize the State of Yu on the way back.

The Duke liked this plan. He sent a special envoy laiden with gifts to the State of Yu to persuade the ruler to allow the Jin troops to pass. However, a sharp-witted official in the Yu immediately smelt a rat and implored the ruler to reject the Duke's request. The official tried to explain that the relationship between the State of Yu and the State of Guo was just like that between lips and teeth. once the lips are gone, the teeth lose their protection and are exposed to the chill of the air.

The ruler of Yu paid no heed to this advice as he was too obsessed with the Duke's gifts. The sharp-witted official warned his close friends that the ruler's decision to allow the Jin troops to pass was sowing dragon's teeth and that he and his family planned to head for the hills.

And so it came to pass, the Jin troops conquered the State of Guo in just a few days and on their way back home captured the ruler of Yu.

I have not been able to think of an equivalent English idiom for 唇亡齿寒. If you think you know one, please let me know.