This allusion is from a folk legend concerning the Eight (Taoist) Immortals crossing the sea at the same time.
八仙过海的典故是个关于八位神仙一同过海的民间传说。
The legend has many versions.
有关八仙的传说，历来不尽统一。
The “eight immortals” are from Taoist mythology and among the best known deities. They are the symbols for good fortune throughout China.
在中国，他们被视为好运的象征。
The earliest descriptions date from the Tang Dynasty (early 7th century),
有关八仙的最早记录出自唐朝，
but their present grouping was not established until the Ming Dynasty (founded in 1368).
而现在的说法则是在明朝形成的，
The immortals are： Zhang Guo-lao, Lu Dong-bin, Cao Guo-jiu, Han Zhongli, Li Tie-guai, Han Xian-zi, He Xian-gu, and Lan Cai-he.
即张果老、吕洞宾、曹国舅、汉钟离、铁拐李、韩湘子、何仙姑、蓝采和八人。
The Eight Immortals are a favorite theme of artists and are portrayed on fans and porcelain.
八仙深受艺术家的喜爱，常被绘制在扇面、瓷器之上。
They also figure prominently in many literary works.
他们也是文学作品中的重要人物。
It is said when they crossed the sea at the same time, each displayed his/her own supernatural prowess.
相传他们八人同时过海时各显神通。
Later, this idiom has been used to refer to those who have their respective means or skills to vie with each other.
后以“八仙过海”比喻处理问题各自有一套办法，或各自显示本领、互相竞赛。
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