The specific definition of truth with-respect-to this post is:

True means that something is in accordance with fact or reality.

Proposition is a statement or assertion that expresses a judgement or opinion (e.g., love leads to happiness).

Truth is a proposition that is accepted as true (e.g., scientific truths; fundamental truths about mankind).

To determine if something is a truth it is necessary to identify the proposition that is to be evaluated and then determine what the evaluation is.  Therefore, there is a difference between what any given person or group says is truth and whether it is truth or not.

Human beings can never know if something is truth.  They can only evaluate the proposition in various situations and assess its truth for themselves.  It is like saying that gravity will always be.  It is our experience that gravity always has been.  Therefore, we conjecture that it will always be.  We go about our lives believing that will never float off from the earth, but we don’t really know for sure what will happen.  In this case, we have scientific evidence that leaves essentially nothing to doubt in this regard, but still there is just what we have learned over time that supports our belief that this is a truth.

Humans interpret the reality around them via their senses.  What they consider to be reality is just an interpretation of reality provided by their senses.  This leads to the sayings:

Truth is in the eye of the beholder.

“Every kind of ignorance in the world all results from not realizing that our perceptions are gambles. We believe what we see and then we believe our interpretation of it, we don’t even know we are making an interpretation most of the time. We think this is reality.”  –Robert Anton Wilson

“We don’t see things as they are; we see them as we are.”  –Anaïs Nin

Knowing truth is subjective.  Care must be taken in believing that we know truth.  It is better to understand our level of certainty of its being truth.  This life must be lived by faith.