We systematically overestimate our knowledge and our ability to predict – on a massive scale. The overconfidence effect does not deal with whether single estimates are correct or not. Rather, it measures the difference between what people really know and what they think they know. What’s surprising is this: experts suffer even more from overconfidence than laypeople do. If asked to forecast oil prices in five years’ time, an economics professor will be as wide of the mark as a zookeeper will. However, the professor will offer his forecast with certitude.
("The Art of Thinking Clearly", Rolf Dobelli)