Dr. Paul Ekman explains why people lie. Read more about reasons for lying including avoiding punishment, harm, or embarrassment.
The lie does matter to them. The number one reason people lie when it just doesn't matter is because they actually do think it matters.
There are several theories for why some people can't stop lying. Narcissists are often pathological liars, because they simply don't care about.
In fact, some people, sad to say, lie almost all the time. Psychologists call these people compulsive or psychopathic liars. They tell lies even when they don't.
Everyone tells a little white lie from time to time. People can lie to protect someone else or to avoid awkward situations, among other reasons.