“Believing they cannot be deceived, they cannot be convinced when they are deceived.”
Exactly! I had an “aha” moment back in about 2003 when I was unable to get an otherwise intelligent young man to concede that there was any possibility that NPR and the rest of the alphabet news outlets lie constantly as a matter of policy.
If he had admitted that, then he would have been admitting that he had been deceived, and he was far too intelligent to be deceived. In effect, my claim was calling him dumb: or, at least, a lot dumber than he thought he was.
Is yours a quotation?
From one of my characters ...