People lie in order to be better fitted in with the demands of mainstream society; to be hypocrite (Pharisee) in a hypocrite world; to gain the most of profit and advantage.
A person lies because s/he doesn't want others to know / sway away their attention from the truth. Whether a person wants to tell lie or not depending on which ethical theory of Kantianism or Utilitarianism s/he is subscribing. Kantianism is about truth is truth whereas in Utilitarianism, truth depends on what net benefits i will get at the end of the day.
In confronting situations all animals resort to Fight or flight.". Other animals have these only. But man has a third one, when he cant do either of the other two; Tell lies, Damned Lies or even corrupted statistics