To be as closely related and interdependent as lips and teeth; to rely on each other for survival or well-being; mutually dependent.
邻里之间应该唇齿相依，互相帮助，共同营造和谐社区。
Neighbors should be as interdependent as lips and teeth, helping each other to foster a harmonious community.
Era:
Ancient
Frequency:
Story:
During the Three Kingdoms period, Emperor Wen of Wei intended to attack the Kingdom of Wu. Bao Xun, a Censor Zhongcheng, advised him, "The imperial army has repeatedly launched campaigns but failed to achieve victory. This is likely because Wu and Shu are as interdependent as lips and teeth, relying on the natural barriers of mountains and rivers, making them a formidable and difficult-to-overcome force."
Instead of considering this sound advice, Emperor Wen became furious and demoted Bao Xun to the position of Zhishu Zhifa Guan.
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