So why do we lie? Sometimes, it's done to embellish the story about the fish that got away. Sometimes it's intended to shelter someone who would be hurt by the truth (i.e., "Yes, Virginia, there is a Santa Claus.")
If an unimpeachable lie detector expert could testify to his results in a one witness versus another case, determining that the victim was truthful and the accused was lying, or vice versa, he essentially would decide the case instead of the jury.
When Falcon let loose the truth on prime time to Wolf Blitzer, even Barney Fife could have figured it out. By his own admission, that was the first moment the light came on for local Sheriff Jim Alderden.