The historian's fallacy is a logical fallacy that occurs when it is assumed that decision makers in the past saw things from the same perspective and with the same information known when later discussing the decision.

Experiments in psychology suggest that people tend to innaccurately remember what turned out to be important as being more important at the time, and have difficulty discounting the advantage of knowing what turned out to have happened. In that discipline the effect is known as hindsight bias.

The fallacy was proposed by David Hackett Fischer , who suggested it was analogous to William James' psychologist's fallacy .

Examples:

• It was a mistake for the United States to arm the mujahadeen in Afghanistan to fight the Russians, because later some of the mujahadeen formed a terrorist group that attacked the United States twenty years later.
• World War I should not have been fought, because it accomplished nothing and led only to World War II.

References

• Fischer, D. H. (1970). Historians' Fallacies: Toward a Logic of Historical Thought. New York: Harper Torchbooks.