Hindsight bias relates to the common expression "hindsight is 20/20.” This expression captures the tendency for people to regard past events as expected or obvious, even when, in real time, the events perplexed those involved. More formally, one might say that after learning the outcome of a series of events—whether the outcome of the World Series or the steps leading to a war—people tend to exaggerate the extent to which they had foreseen the likelihood of its occurrence. It is the tendency to exaggerate, after learning an outcome, one's ability to have foreseen how something turned out. Also known as the I-knew-it-all-along phenomenon.