Recollection or reevaluation of past events can be affected by what has happened since. In particular, once people know the outcome of an event, they tend to overestimate what could have been anticipated in foresight. This effect has been termed hindsight bias or the knew-it-all-along effect.

Two different general experimental procedures are usually employed. In the memory design, people first give an (unbiased) answer, then receive the solution and are finally asked to recall their earlier, original answer. In the control situation, the same items are given to other people without providing them with the solution before they recall their original answer. In the hypothetical design, people receive the solution right away and are then asked to provide the answer they would have ...