It's one of the Ten Commandments: Do not lie.
As a child I got a pretty graphic example from a nun of why lying is unwise.
She said if you tell a lie you will have to tell nine more lies to cover up that one lie, and for each of those nine lies you tell, you will have to tell nine more, and for each of those you will have to tell nine more, and so on.
“You 0can't keep track of all the lies, so you will be caught,” she said.
I have a whole new perspective on lying.