Harry Beckwith in his landmark book Selling the Invisible (Thomson Texere, 2001) comments on the Overconfidence bias.  From pages 74-75 of the book I’ll quote and paraphrase him:

“On answers of which people say they are totally – 100 percent – certain they are right only 85 percent of the time. In other words, 15 percent of the time you think you are absolutely certain you are absolutely wrong.Continue reading