expression
clear as day; patently obvious
Idiomatic expression emphasizing that something is so obvious it is like watching a fire. Often used for negative situations or consequences that are unmistakable.
彼が嘘をついているのは火を見るより明らかだ。
It's as plain as day that he is lying.
このままでは失敗するのは火を見るより明らかだった。
It was patently obvious that we would fail if things continued like this.
明らか is a general adjective meaning 'clear' or 'obvious', while 火を見るより明らか is a fixed idiomatic expression that intensifies the obviousness with a vivid simile.
A set phrase literally meaning 'clearer than watching a fire', used idiomatically to express extreme obviousness. The exact origin is uncertain, but it likely arose from the universal experience that fire is immediately visible and unmistakable.