The fallacy of identity is one example of how our analytic skills are often incapacitated because our thinking is predisposed to look for linear relationships and disregard non-linearity. The fallacy of identity, according to a historian David Hackett Fischer, is the idea that effects must somehow resemble its cause. One common form of this fallacy is the idea that big events must have big consequences, and small events small consequences. Another form is the idea that cause and effect must be similar in type or nature.
Causal Magnitude and Proportionality
A basic form of this fallacy is the assumption that big events must have big effects, and conversely, small events must have small effects. Yet, human history is full of examples of how big events failed to produce big consequences. Fischer points out one example from historical analysis: the English defeat of the Spanish Armada in 1588. Many historians mistakenly looked for some major effects of this event because of the fallacious assumption that such a big event must have produced big effects. But it didn’t. By 1603, Spain hadn’t lost a single overseas outpost and afterwards the British naval superiority not only didn’t increase but even slightly decreased.
Of course, the converse is also true: a very small event may bring about massive changes. The best example is the popular butterfly effect in the chaos theory: the flapping of the wings of a butterfly may cause different hurricane formations several weeks later.
Such non-linearity, unfortunately, runs against our analytic predispositions. This also applies to professional analysts, who usually fall for this fallacy searching for large causes and disregarding small ones. Even professional intelligent analysts are likely to fall for this bias, albeit to a lesser degree, when trying to come up with proportionally matching causal explanations of an event. This bias, of course, is most pronounced with analytically less inclined people, such as conspiracy theorists who refuse to even entertain a possibility that small, trivial, random factors could be responsible for large effects (such as a lone and measly shooter killing a president or another key figure, thus possibly changing the world history).
The Tunnel Form of Causal Resemblance
Another form of this fallacy is the mistaken assumption that effects must resemble their causes not only in size, but also in type or nature. For instance, people assume that religious phenomena are driven by religious origins, that economic effects must have economic causes, and so forth. Yet, this is often not the case. For instance, primarily non-religious causes (poverty or other economic issues) may bring about large religious changes, or primarily religious causes may bring about large economic or political changes.
The basic takeaway from the fallacy of identity is to avoid making automatic assumptions that effects must match their causes in either magnitude or type. Of course, often they will match and there may be a perfect proportional relationship between causes and effects. Yet, to improve our analytic thinking, we should always be on the lookout for non-linear relations. When analyzing a situation, we should realize that random factors, small mistakes, and other trivial events may bring about large social, political, and economic effects. Conversely, we should also guard against this bias by realizing that considerable events may have no considerable effects, and that we may be inclined to attribute large effects even when there none.
 David Hackett Fischer, Historians’ Fallacies: Toward a Logic of Historical Thought (NY: Harper Perennial, 1970) p. 177.
 Ibid, at 166-167.
 Richards J. Heuer, Jr., Psychology of Intelligence Analysis (Center for the Study of Intelligence, Central Intelligence Agency, 1999) p. 134.
 Ibid, at 133.