People tend, with the benefit of hindsight, to falsely believe that they would have predicted the outcome of an event. More colloquially, hindsight bias could be called the "You should have known all along" phenomenon. In the context of litigation, it can lead juries to find defendants which took reasonable care negligent or even reckless. The mere fact that an injury occurred is enough to conclude that the defendant should have known that an injury would occur.



The hindsight bias is not just a theory. It has been empirically demonstrated over and over again. In one study, based on the well-known case, Petition of Kinsman Transit Company, the researchers, Kamin and Raschlinski ["Ex Post is not equal to Ex Ante: Determining Liability in Hindsight," 19 Law and Human Behavior 89 (1995)], asked college students to judge whether or not a city was negligent in failing to hire a bridge operator during the winter when the danger of flooding was small.

In one condition (the hindsight condition), the subjects were told that there had been an accident that would not have occurred had there been a bridge operator. Fifty-seven percent of the subjects decided that the city was negligent. In the other condition (the foresight condition), in which subjects were not told about the accident, only 24% said the city was negligent.

The hindsight bias is very difficult to overcome. For instance, educating people about the bias does nothing to remove it. Jeffrey Rachlinski ["Heuristics and Biases in the Courts: Ignorance or Adaption?" Cornell Law School Working Papers, Fall (1999)] has argued that the courts implicitly recognize the hindsight bias by, for instance, suppressing evidence such as subsequent remedial measures in negligence and product liability cases, allowing the use of custom as a defense in medical malpractice cases, and the business judgment rule in corporate cases. But the evidence is still that jurors will be affected by the hindsight bias in their decision-making.

We are all subject to the hindsight bias. The testimony of expert witnesses is cemented in the idea that outcomes were inevitable or foreseeable. Professor Arkes of Ohio State has proposed that experts in medical malpractice cases give their opinions without knowing how events turned out (BBC News Online, February 2, 2000). This will never happen, but it is an intriguing idea.

The only way in which hindsight bias has been reduced is by giving people detailed explanations for how alternative outcomes might have been obtained and how, with foresight, those outcomes were plausible ones.