(idiomatic) the fish rots from the head

something or someone small or insignificant among great things or people; a fool among sages

fishfinder

(mahjong) winning off the final discard before reaching the dead wall, worth 1 翻 (han, “double”)

(figuratively) being carefree and unaware of an imminent danger

(figuratively) larger-than-life characters do not associate with unnoteworthy characters, nor do they concern themselves with trivial matters / (literally) boat-swallowing fish do not swim in tributaries