Wizard's First Rule:
People are stupid, they will believe something because they want it to be true; or they're afraid it's true.
Given proper motivation, almost anyone will believe almost anything. Because people are stupid, they will believe a lie because they want to believe its true, or because they're afraid it might be true. Peoples' heads are full of knowledge, facts and beliefs, and most of it is false, yet they think it all true. People are stupid; they can only rarely tell the difference between a lie and the truth, and yet they are confident they can, and so are all the easier to fool.
On a slightly related note, Sword of Truth Series = My favorite Series ever, tied with the Sword of Shannarah Series.
Y'all be banned if ye haven't read either of them.