"(as|) plain as the nose on {one's} face"의 정의 및 의미

What is the origin of the idiom "plain as the nose on one's face" and when to use it?

The origin of the idiom "plain as the nose on one's face" lies in the undeniable visibility and obviousness of one's facial features. The phrase signifies that something is extremely clear, evident, or easily discernible, much like the unmistakable presence of a person's nose on their face. It is primarily used to emphasize the lack of ambiguity or complexity, suggesting that the truth or reality of a situation is readily apparent and requires no further explanation.