This is an awesome thread that really had me thinking.
We know they lie about anything and everything. As a logical, truthful human being, it makes no sense to me that mine would lie about the town he now lives in of where he left his cigarette lighter last Friday (either in his truck or at his house depending on which time be borrowed mine).
The ultimate question is why they do this, and the responses on this thread are leading my to numerous conclusions.
1. They are emotionally immature. Kids and teenagers lie to protect themselves from the consequences of their behavior. That, at least, makes sense when we consider the lies about OW/OM.
1a. Because they believe we are evil incarnate bent on taking away everything they know they deserve, they lie even more to try to ensure we don't do that. Mine honestly had himself convinced that I would do everything in my power to ensure he couldn't become part owner of an airplane. Not the case. In fact, after giving lots of thought to the stupid thing, I want him to have it as long as it doesn't ultimately destroy me financially. They have others chirping in their ears telling them what our motivations are. Others who have never met us or who have no way of knowing what we think or feel. Others who are probably projecting and have an agenda. So, again, it's about self-protection. They lie because they are so weak they are influenced by the agendas of others.
2. They feel entitled to whatever they feel entitled to (see the link from Stillpraying) and will do anything and everything, including lie, to get it and, IMO, avoid the consequences. See #1.
3. They are trying to escape who they are, so they create a new persona, which is at least part a lie itself. They need to be better, stronger, faster than they were before. But that necessitates lies because they seem to believe they are worse, weaker, and slower than they were before. So they lie to make themselves more interesting, etc. Thus Law, 3, and I all have husbands who have embellished their military careers.
4. Lies are among the stepping stones to their self destruction. As frustrating, annoying and infuriating as they can be to us (seriously, lying about what he had for lunch? About your wife having a brain tumor?), they are necessary because all those lies are going to come back and bite them in the a$$. They know the truth (or should--with MLC brain, that's a crapshoot). But they are compelled to destroy themselves, and the lies hell them do that.
4a. In order to self-destruct completely, they must lie in order to push us away, just as they must be cruel to us so they can escape. Like OffRoad, I get of lies of omission. Somewhere deep down, mine seems for me to want to know the truth but is too much of a coward to tell me. He drops hints and clues so I can figure stuff out. When he does that, the guilt oozes from him because the omissions are always about big things such as him living with OW. I believe, at least with mine, a component of this is related to #1a: they believe we are horrible and out to make their life miserable, but like children, they actually do want to confess the truth. They just can't.
I may be entirely wrong about all of this, but it makes a lot of sense to me. For me, its hard to separate out the various strands of why they lie since everything is so interconnected. Ultimately, though, I am believing the lies are a compendium of the need to destroy themselves as well as some convoluted sense of self-preservation.
Now to figure out why someone would need to preserve himself for shopping at Costco.
Unless that shopping is on a Saturday afternoon. That, at least, I get.
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Pathological liars?