Characters
Jerry, just remember, it’s not a lie if you believe it.
— George Costanza
Behind the line May contain spoilers.
Our reading
An editorial interpretation.
This is comic self-deception offered as advice: if you truly believe something, it stops being a lie. The joke is that it treats sincerity as a loophole, ignoring that being convinced of something doesn't make it true, and it's delivered with total confidence.
Context reviewed