Do we really need a study on why people lie? They lie because it's easy, and cowards are good at "easy." Telling the truth takes moxie, and few have it.
If we suspect that a man is lying, we should pretend to believe him; for then he becomes bold and assured, lies more vigorously, and is unmasked.
Cathy's lies were never innocent. Their purpose was to escape punishment, or work, or responsibility, and they were used for profit. Most liars are tripped up either because they forget what they have...
I deny the lawfulness of telling a lie to a sick man for fear of alarming him you have no business with consequences you are to tell the truth.