…termed the hindsight bias, or the “I knew-it-all-along” effect. As you may recall from our discussion in Chapter 1, once we know the outcome of an event, we have a strong tendency to believe that we could have predicted it in advance. In the Fischhoff experiments, subjects were given a test assessing their knowledge of historical events. The subject’s task was to indicate the likelihood that four possible outcomes of the event could have actually occurred. Some of the subjects were told that one of the four possibilities had actually happened but were asked to make the estimates that they would have made had they not first been told the “right” answers. The results showed that subjects could not ignore this information; they substantially overestimated their prior knowledge of correct answers. In other words, even though subjects really didn’t know the answers to the test, once they were told an answer, they believed that they knew it all along and that their memories had not changed.
Excerpt from: The Social Animal by Elliot Aronson and Joshua Aronson