A term that when prefixed to a statement does more damage than good. Its purpose is to state that you are about to tell the
truth about something. However, If one has to use this statement, it can be concluded that when that same person does not use this statement then they are lying, because when they are telling the
truth, they state that they are about to tell the
truth by saying, "I’m not gonna
lie..."
So this statement, in effect, when used, devalues any potential credibility one once had as an honest and truthful person when they are not using the statement.
It is synonymous with: to tell you the
truth, honestly, actually, as a matter of fact, in fact , truthfully