The question of, is an interesting question no doubt, and is a question that goes back to the very beginning of human relationships. First of all, it pretty obvious that lying is a form of self protection. It is quite possible that lying evolved in this way. If you think about it, if the caveman made a mistake when hunting that potentially could destroy the chances of his tribespeople getting food for the week, and he had to report back to the tribal leader, lying could potentially save his life!
Obviously lying in this day and age, is quite often used by people for much less serious situations. And can become quite a negative habitual pattern for many people. Basically it comes down to win a person not wanting to deal with a certain situation, and the choice of lying, being an easy way out. It’s about not wanting to feel pain, and avoidance.
Obviously the reasons why people lie, are very situation will, and really do depend on the context of the situation. For that reason it is very difficult to say why people lie in general, apart from what we have discussed above. I believe that lying can be positive, if used to protect someone else, instead of being used to protect oneself because one did not do the right thing or created a bad situation through not being responsible.