You're more certain than you have any right to be

Ask people how confident they are in an answer, and their stated certainty routinely outruns how often they're actually right. In classic calibration studies, people who said they were '100% certain' were wrong roughly one time in five. The gap between confidence and accuracy is widest on hard questions, where people should be most cautious.

— Baruch Fischhoff, Paul Slovic, Sarah Lichtenstein, Knowing with Certainty: The Appropriateness of Extreme Confidence Judgments — Journal of Experimental Psychology: Human Perception and Performance, 1977