You're supposed to PRETEND the narcissist's lies are true.

Puglette recently commented on a post:

They will say ANYTHING and tell any outrageous lie, and if you can prove it's all BS, somehow YOU are the "bad guy" for not being gullible and believing their reality.

True. This is another bizarre thing about narcissists -- something no normal person would even think of doing.

It reminded me of an example at Joanna Ashmun's site Narcissistic Personality Disorder: Traits Discussed

Appearances are all there is with narcissists -- and their self-hatred knows no bounds. The most dramatic example I can think of is from John Cheever's journals. Throughout his life he had pursued surreptitious homosexual activities, being transiently infatuated with young men who reminded him of himself in his youth, while also living in a superficially settled way as a married family man, a respected writer with an enviable suburban life, breeding pedigreed dogs and serving on the vestry of the Episcopal church. When his secret life (going to New York City for a few days every now and then to pick up sailors and other beautiful boys for brief flings) came to scandalous light, his family sought to reassure him by telling him that they'd known about his homosexual activities for years. Now, a normal person would be ashamed and embarrassed but also relieved and grateful that scandal, not to mention chronic emotional and marital infidelity, had not caused his wife and children to reject and abandon him -- but not the narcissist! Oh, no, Cheever was enraged that they would ever have thought such a thing of him -- if they really loved him, they'd have bought his artificial "country squire" persona: they would have seen him as he wished to be seen: they would have believed his lies without question or doubt.

I have noted a similar phenomenon in What Makes Narcissists Different:

Another big difference between narcissists and normal people when they're projecting on you is that narcissists expect you to share their delusion. ... The narcissist wants you to identify with the image he projects on you. You are a mirror to reflect his fantasy, so he pressures you to behave as though it is real. ... Narcissists do not connect with reality: appearances are all that matter in their world. So, you can lay out your grievances to a narcissist in a letter to let him know what you think, but if tomorrow you encounter him and act as though none of it happened, he is perfectly satisfied.

Putting all three of those examples together eliminates all but one possible explanation. Narcissists don't tell lies because they want you to believe them. Why should they? You are just an object to them. Like a chess piece or a hammer. They are unaware of the thinking person inside you. Just ask a narcissist what he or she thinks you think. They'll look at you as though you just asked them what they think that elm tree over there thinks. No kidding, that question will crash a narcissist's brain.

They tell lies because they aren't living in the real world. They are living in a fantasy, a work of fiction, a stageplay that they make up as they go along. They are just mental children playing "pretend." You are supposed to play along and pretend that their lies are true. Because they are the author of The World According to Them, and you are supposed to follow their script. Period.

And these mental children get very mad if you don't.

Unbelievable? Then wait a minute. Think again. We've all done this and seen others do it. Back when we were three or four years old.

Yes, remember being a little child? Notice that the narcissist is acting EXACTLY like a four-year-old who says to his friends, "Let's play army. Here is your gun." And he hands his little friend a tennis racket. If the friend says, "But this is a tennis racket, not a gun," the Pretender gets very mad at him for not playing along.

Pretender doesn't want his playmate to THINK it's a gun; he wants his playmate to ACT as though it's a gun.

That's exactly what an adult narcissist is doing when he lies -- just pretending. He has substituted fantasy for reality, because he can control an imaginary world. So, when we say that narcissists are mental four-year-olds, we are NOT just making an analogy: we are stating an exact fact. They have never mentally matured past that stage. They are as deep into fantasy as a child with an imaginary friend, a child who insists that you set a place for that friend at the table.

In other words, narcissists don't care whether you believe their lies. They don't care what you think. Appearances are all there is with a narcissist, so all they care about is how you ACT.

They just want you to ACT as though their lies are true. Why? Because if you don't, you are challenging their delusion, reminding them that it isn't real = you are making it hard for them to continue deluding themselves.

So, you're a naughty toy if you catch them in a lie: you're not supposed to do that: you're supposed to play along and pretend the lie is true.

This is no minor matter. The failure to mentally mature is a serious mental defect.

See also The Narcissist as Patholigical Liar and The Narcissist's Script.