Why do People Lie?

A couple of days ago I was at the library when a radio presenter walked up to me armed with a list of questions ready to unload them on anyone willing to respond. ‘Why do people lie?’ was his topic question. Well, first off I was not prepared to answer. I would have been grateful to read through his questions prior to the interview. You see, I like to sound intelligent-which we all know, I am.
I have never been on radio before therefore the prospect made me rather anxious. A very large part of me wanted to turn down his request but somewhere deep down, I lusted to be aired. I thought it would be a great experience. A few seconds, maybe a minute on air? I figured it would not hurt. I went for it!
My answer to his question was simple. Lying is something that is inside of us all. We have it from when we are born. That explains why our parents will tell us from infantry that lying is bad, that you have to tell the truth. We have to be trained to run from lying, to despite it, to always expect the truth. What I am saying is lying is innate but we can break free. We choose to rise above it. With good upbringing and constant practice, lying could become a tremendous task.
So what is your opinion? Why do people lie? Is it ok to lie in any case? Why or why not?