Well, they are.
Who doesn't know the pleasure of telling a small child that you've got candy for him and then watching his face fall when he realizes that you don't?
Who hasn't felt that secret thrill when you tell the accident victim that you're calling an ambulance when you're just going out for a Coke?
Show me a heart so hardened to fun that they haven't said "I love you" to their significant other... and then gone out to sleep with someone else?
Lies are fun!