A possible reason that explains why some people lie

Some people just have an indescribable aversion to communicating the real reasons behind their actions.

Why?

My educated guess as to why is that, is that when they were kids and they spoke their mind, they got beaten, scoffed at, yelled at or otherwise emotionally abused.  So they developed compulsive lying as a coping mechanism that kept them out of the psychological pain they endured when they told the truth.  And that defense mechanism persists in adulthood.  I know a few people like that -- they'll say anything, even the craziest shit, if it causes anybody to back off who is asking about what's really on their minds.

Those kinds of people are damaged goods -- you do not want to be in a relationship with them, not as business partners, not as lovers, not as friends, not as family.

Childhood circumstances, of course, do not stop the hammer of adult morality.  While I recognize that their modus operandi is a mechanism they learned to cope for their circumstances when they were young, of course, as adults, those circumstances do not excuse them from the moral responsibility of their wrongs (specifically, for the lies and omissions they tend to engage into).

I might be wrong about this, of course, but my observations about liars fit 100% with this hypothesis.