Words Have Inherent Trust

I still struggle with having my characters lie. I can have them do it, but it always confuses my readers. For so long, I thought it was a failing in my skills (and I still think it is to some degree), but I realized why it is such a struggle in the first place. Words have inherent trust.

I'm not sure why, but I find that we always believe characters in stories. They always have a certain wholesomeness, where they always speak from the heart and it is always true. In fact, the only way we can ever seem to accept a character telling a lie is when they explicitly say they are going to lie, or if they use the most ridiculous, cartoonish motions and inflections that nobody would ever use in real life if they were actually trying to deceive someone.

My favorite example of this is in the movie The Dark Knight, where The Joker tells the story of how he got his scars. When we hear it, it sounds perfectly reasonable, so we assume he is being sincere. Later in the movie, he tells the story of how he got his scars, and it is a completely different story. Nothing is the same at all in it. The audience often scratches its head at the incongruence. They usually figure out that he's lying, but the question they ask is, "which story was the lie?" The point being, they still think that one of them is the truth. The idea that they're both lies doesn't seem to cross many people's minds.

Ultimately, the problem I have is that I am trying to overcome a very human assumption. I still think it can be done without resorting to cheap gimmicks, but I wonder how much of the burden is on my skill and how much of it is hoping that my audience will figure out that inconsistencies are the result of characters lying and not of being a bad author.