Pants on Fire!

I don't understand why people lie. Specifically, people who lie just as easily as saying "hello".  Is it easier than telling the truth for some reason?  Perhaps they can't remember something, so they make something up to fill in their memory lapses?  I can understand fudging something a bit if the truth would do unnecessary harm, but not if it's just for the convenience of the liar.  While I might think a bit less of someone if I know the truth, when I uncover the lie (I have an excellent memory, so I usually do) I think even less of them because I really dislike liars.  I've recently been informed that someone, who I know is a liar because they lied to me and I found out, is telling lies about me to other people.  Is it worth it to confront the situation?  Probably not, it would most likely just result in more lies.