This is perhaps the best articulated reason on why people lie.
Why do we tell lies? We lie to evade reality; we lie because the truth is too painful or too shameful for us to face, or because the truth is simply inconvenient and has to be suppressed before it’s allowed to disturb us. We invent lies because, for whatever reason, we want to invent reality. And the false reality which we invent, the world we make up by our lying, has one great advantage for us: It makes no claims on us. It demands nothing. It doesn’t shape us in the way that truth shapes us; it faces us with no obligations; it has no hard, resistant surfaces which we can’t get through. A lie is a made-up reality, and so never unsettles, never criticizes, never resists, never overthrows us. It’s the world, not as it is, but as we wish it to be: a world organized around us and our desires, the perfect environment in which we can be left at peace to be ourselves and to follow our own good or evil purposes.
Lies are a desperately destructive force in human life. When they take the form of private fantasy, they rob us of our ability to deal truthfully with the outside world; but when lies go public, when an entire social group replaces reality with untruth, then the consequences are deadly. Sometimes, indeed, they can be literally deadly: Lies can kill. Lies work only when they remain unexposed. Once truth is allowed out, once reality is let in, then the lie just vanishes; the whole world of falsehood just crashes to the ground. And if the lie is to be maintained intact, then anything which speaks the truth has to be got rid of.
Totalitarian societies, dishonest businesses, abusive human relationships – they all depend on the exclusion of truth and truth-speakers, making sure that what really is the case isn’t allowed to come to light. Lies only work when they aren’t shown up for what they are; and that’s why lies always breed more lies, as we try to protect the world we’ve invented from being exposed (John Webster, Confronted by Grace [Bellingham: Lexham Press, 2015], 5-6).