Hindsight Bias

What Is Hindsight Bias?

In hindsight, people consistently exaggerate what could have been anticipated in foresight. They not only tend to view what has happened as having been inevitable, but also to view it as having appeared “relatively inevitable” before it happened. They even misremember their own predictions so as to exaggerate in hindsight what they knew in foresight (Fischhoff, 1975).

Hindsight bias is the tendency to see a given outcome as inevitable once the actual outcome is known. In other words, hindsight bias is the tendency to be wise after the event. It is captured in common phrases like “I knew it all along” and “Hindsight is 20/20.” Consider the cognitive exercise in Exhibit I.

Exhibit I, The Hindsight Bias: I Knew It All Along
Think about a recent test that you took in a challenging course (and for which you have received your grade). How predictable in advance was your performance? If you had been asked before the test to predict your grade, what would you have said?

According to research in social and cognitive psychology, you are likely to think now that your performance was more predictable than it actually was. That is, you probably now think that if you had been asked before the test to predict the grade, you would have predicted a grade relatively close to the one you actually received. But if you had really been asked before the test, you would have expressed more uncertainty about how you would do.

What is different between now and before the test? You know how you did. This “outcome information” is very difficult to ignore and colors your judgment of what you believed before the event, a phenomenon known as hindsight bias (Fischhoff, 1975).

The hindsight bias (also called the I-knew-it-all-along phenomenon) means that we see whatever event occurs as completely in line with our expectations, even if we would have seen a completely different outcome as also in line with our expectations (Hawkins & Hastie, 1990).

In a study designed to demonstrate the power of the hindsight bias, students read about a dating situation that ended in one of two ways—with a marriage proposal or a rape (Carli, 1999). Although the story was exactly the same in the two conditions (except for the last line), people saw the ending as rather predictable in both situations, based on the details of the story (which of course were the same in both conditions).

Why do people make this error?

In part because they misremember details that support their argument. In other words, we fill in blanks in our memory with things that seem to make sense. Several processes might also contribute to the hindsight bias, but we will mention just two.

One important cause is that people reinterpret pre-outcome information based on knowing the outcome. If you learn that a friend has dropped out of school, you might reinterpret his or her past behaviors as reflecting unhappiness or disillusionment. These reinterpretations make it seem more obvious that the decision to drop out would happen.

Second, people generate explanations that would not have occurred to them if they had not known the outcome. You might think about your friend’s academic history and realize that his performance has been declining since starting college. This realization might lead you to conclude that poor grades caused your friend to drop out and his decision was foreseeable.

Hindsight bias also influences how we perceive numerous real-world events. In one study, researchers examined students’ predictions about whether then-President Clinton would be convicted in his impeachment trial in 2001 (Bryant & Guilbault, 2002). As predicted, after his acquittal students reported having believed all along that he would not be convicted, even though before the announcement of his acquittal they saw conviction as rather likely.

Similarly, after the tragic events of September 11th, many people saw the hijackings—and crashes—that occurred as caused by the now seemingly obvious need to lock cockpit doors on airplanes. But we need to remember that in all previous instances, hijackers were motivated by a desire to have the plane land safely… and people never imagined that hijackers would both be able to fly planes and intend to deliberately crash them.

Another domain in which the hindsight bias may occur is accusations of medical malpractice. If a patient has been seen by a physician but then suddenly deteriorates, his or her family may later look back and conclude that the correct diagnosis was obvious, whereas it may actually have been unclear. Although it is flattering to believe that we would have known all along what we could only know in hindsight, that belief hardly affords us a fair appraisal of the extent to which surprises and failures are inevitable.