I am convinced that, where men are the most sure and arrogant, they are commonly the most mistaken, and have there given reins to passion, without that proper deliberation and suspense, which can alone secure them from the grossest absurdities.
 David Hume, An Enquiry Concerning the Principles of Morals (1751). copy citation

Context

“I am sensible, that nothing can be more unphilosophical than to be positive or dogmatical on any subject; and that, even if excessive scepticism could be maintained, it would not be more destructive to all just reasoning and inquiry. I am convinced that, where men are the most sure and arrogant, they are commonly the most mistaken, and have there given reins to passion, without that proper deliberation and suspense, which can alone secure them from the grossest absurdities. Yet, I must confess, that this enumeration puts the matter in so strong a light, that I cannot, at PRESENT, be more assured of any truth, which I learn from reasoning and argument, than that personal merit consists entirely in the usefulness or agreeableness of qualities to the person himself possessed of them, or to others, who have any intercourse with him.” source