In a very general sense, 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.

In the context of safety analysis, hindsight bias refers to the tendency to judge the events leading up to an accident as errors because the bad outcome is known. The more severe the outcome, the more likely that decisions leading up to this outcome will be judged as errors. Judging the antecedent decisions as errors implies that the outcome was preventable. In legal circles, one might use the phrase "but for," as in "but for these errors in judgment, this terrible outcome would not have occurred." Such judgments return us to the concept of "hindsight is 20/20." Those reviewing events after the fact see the outcome as more foreseeable and therefore more preventable than they would have appreciated in real time.

August 1, 2019