Chinese and American Sayings

Rebecca is my dear sweet niece from China that is visiting for summer vacation. She says she is very “Cool” and she wears jeans with holes in them so I guess she is cool indeed. Anyway here is a little story from her to me today.

Rebecca says, “The lips live with teeth”. This is a famous Chinese saying meaning what? Rebecca says, “If you let your neighbor country be attacked without helping and the country falls to its enemies then you will be next to be attacked. So the moral is that when your neighbor meets difficulty you must help.” This is her explanation for why China helped Korea during the war with the US. Now I am really confused.