It's not a "fact" in the sense that's its truth is beyond question.
It's admissible, if it's relevant, and not barred by the rules of evidence.
It's not due any particular weight by itself, i.e., the "fact" can be contradicted by other facts in evidence, and the witness's truthfulness, his ability to observe, or to recall, all are subject to impeachment on cross-examination.
Virtually every inadmissible oral hearsay statement is witnessed (heard).
Witnessing a statement doesn't make it non-hearsay.
Hearsay statements cannot be used to prove the truth of the matter stated.
"I want to die" can't be used to prove she wants to die.
So then you are saying that it was admitted as credible because no one else gave testimony to the contrary?