FACT: a thing that is indisputably the case.
If you are unable to accurately identify what a fact is in the context of an investigation (any investigation), you will have no objective basis for evaluating the reliability/explanatory power of any truth claims or theories.
Inferences, interpretations, claims, theories, and testimonies are fallible and easily incorporate error. If any of these are used to evaluate the reliability of truth claims, one runs the risk of attempting to judge what is true by what may very well be false, an exercise in futility.
Only when facts are used as the “ground floor” for evaluating truth claims and theories can the core set of objective criteria be properly applied (logical consistency, coherency, and external correspondence).