You Don't Know What The Truth Is

You don't know what the truth, the whole truth and nothing but the truth is.
plural truths
1 a archaic : fidelity, constancy b : sincerity in action, character, and utterance2 a (1) : the state of being the case : fact 
(2) : the body of real things, events, and facts : actuality (3) often capitalized : a transcendent fundamental or spiritual reality b : a judgment, proposition, or idea that is true or accepted as true <truths of thermodynamics> c : the body of true statements and propositions
  1. Do you swear to tell the whole truth and nothing but the truth?
  2. Her story contains a grain of truth but also lots of exaggeration
the truth - what the witness experienced
the whole truth - not leaving any material out
nothing but the truth - definitely no lies