In the legal realm, witnesses in a trial vow to speak the truth, the whole truth, and nothing but the truth. Then the attorneys, both the prosecution and the defense, attack the truth-telling of those witnesses, demonstrating the difficulty of defining TRUTH.
To be able to call something "the truth" requires at least some background in ontology (the study of being) and epistemology (the study of knowledge). It is very humbling to try to tease the truth out of our flawed perceptions. There are only two possible “ultimate” truths: (1) Natural /physical /material origins, or (2) Supernatural origins.
Faith plays a role in our interpretation of what's true to us. The Bible tells us about faith in Hebrews 11:1, "Now faith is the assurance (substance) of things hoped for, the conviction (evidence) of things not seen." Without ultimate truth, it is impossible to tell the “whole truth” about anything.