In order to survive, troubled fish wet each other's bodies with foam in their mouths. Later used to refer to the feelings of husband and wife, can also be used for friends.
Metaphor is to help each other with meager strength in difficult situations. The original text is from Master Zhuangzi. "When spring is dry, fish are on land, wet and wet. It's better to forget each other in Jianghu. It is better to get carried away than to be arrogant. " .
There is a paragraph behind, "Fish makes water, and man makes pottery. Those who make water together are fed through the pool; People who create Tao are born with nothing.
So fish forget rivers and lakes, and people forget Taoism. "