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.
It's as plain as day that he is lying.
It was patently obvious that we would fail if things continued like this.
Standard kanji spelling for this idiomatic expression.
Kana spelling of the first character is sometimes used for readability.
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.