To face the facts is to accept the truth of a situation you have been avoiding. The bank statement is on the table and you finally read it.
The definite article and the plural are both fixed — face a fact is not the phrase. It nearly always arrives as an instruction, to yourself or to somebody who has been putting it off, which gives it a bracing, slightly unkind tone. Face up to is the version that takes an object, and let's face it is the conversational cousin used to introduce something everyone already knows.
1phraseface the factsTo accept the truth of a situation.
“Sooner or later you have to face the facts.”
face the facts is an act of accepting reality.
Practised in Common Word Pairs