This is the terrible effect of Radical Skepticism, the epistemological view that you cannot trust anyone to tell you the truth. It destroys the ability to learn from civilization, and even can invade one's view of family members. It finally short circuits into Solipsism, where one's own mind is held as the ultimate reality. This is a break with reality that is the basis of psychosis. I think a lot of it is fueled by foolish pride: "I'm too smart to be fooled, and I can tell that everyone is lying to me."