The characters combine literally and directly to tell the story: “Eight Immortals cross the sea.” The profound metaphorical meaning is derived entirely from the famous legend associated with this phrase.
The idiom is rooted in the popular stories of the Eight Immortals, a group of legendary figures in Chinese mythology and Taoism. These figures (He Xiangu, Cao Guojiu, Li Tieguai, etc.) represent a cross-section of society: male, female, old, young, rich, poor, noble, and commoner. Each has a unique backstory, personality, and a magical instrument. The legend of “crossing the sea” tells of a time they decided to travel to a feast. Instead of using their usual method of transport (like riding on a cloud), the immortal Lü Dongbin suggested that they each use their personal powers and magical items to get across the East Sea, making for a more interesting journey. This act became a powerful symbol of showcasing individual prowess.
This phrase is common in both formal and informal contexts. It carries a positive and dynamic connotation, often used to encourage or describe a situation filled with talent and energy.
A very common extension of the phrase is “八仙过海,各显神通” (bā xiān guò hǎi, gè xiǎn shén tōng), which means “The Eight Immortals cross the sea, each showing their divine powers.” The second part, 各显神通, explicitly states the meaning implied by the first.