They imitate over and over again the first liar. One does not need to be taught to lie. Lying is a by-product of sin. It was the lie that set the trap capturing the first sinner. Eve succumbed to the lie.
Truth never changes and never requires a change.
The truth is, one does not have to lie. But all do lie or at some time have lied. The most revealing way is to lay the lie next to truth. Yet, even this way is not always conclusive because of the very nature of the lie. The lie most efficiently employed, requires that it be adorned with a certain degree of truth.