The phrase 相濡以沫 is formed from an allegorical tale in the Zhuangzi, where two stranded fish moisten each other with saliva to survive. The characters sequentially construct this image: 相 (mutually) establishes reciprocity, 濡 (to moisten) denotes the action, 以 (with) introduces the means, and 沫 (foam/saliva) specifies the substance used, thereby literally depicting mutual sustenance in adversity.