How We Know What Isn't So: The Fallibility of Human Reason in Everyday Life

by Thomas Gilovich

Today, more people believe in ESP than in evolution,4 and in this country there are 20 times as many astrologers as there are astronomers.

We are predisposed to see order, pattern, and meaning in the world, and we find randomness, chaos, and meaninglessness unsatisfying. Human nature abhors a lack of predictability and the absence of meaning. As a consequence, we tend to “see” order where there is none, and we spot meaningful patterns where only the vagaries of chance are operating.

Representativeness can be thought of as the reflexive tendency to assess the similarity of outcomes, instances, and categories on relatively salient and even superficial features, and then to use these assessments of similarity as a basis of judgment.

Among other things, to reiterate, representativeness leads to the belief that causes resemble their effects: Big effects should have big causes, complex effects should have complex causes, and so on. This assumption contains some truth, and so it generally facilitates causal reasoning by narrowing the number of potential causes to consider. But not all causes resemble their effects (again, tiny viruses cause enormous epidemics), and an over-reliance on this assumption can lead people to ignore important causal relations and to “detect” some that are not there. Thus, the very same principle that permits us to make judgments with apparent ease and considerable success can also be responsible for some of our systematic errors.

belief, people are inclined to see what they expect to see, and conclude what they expect to conclude. Information that is consistent with our pre-existing beliefs is often accepted at face value, whereas evidence that contradicts them is critically scrutinized and discounted. Our beliefs may thus be less responsive than they should to the implications of new information.

how even-handed we should be in evaluating evidence is rather complex. Not all bias is a bad thing; indeed, a certain amount is absolutely essential.

I have argued that people often resist the challenge of information that is inconsistent with their beliefs not by ignoring it, but by subjecting it to particularly intense scrutiny.

people do not realize that the [inferential] process is biased by their goals, that they are only accessing a subset of their relevant knowledge, that they would probably access different beliefs and [inferential] rules in the presence of different goals, and that they might even be capable of justifying opposite conclusions on different occasions.”

Our motivations thus influence our beliefs through the subtle ways we choose a comforting pattern from the fabric of evidence. One of the simplest and yet most powerful ways we do so lies in how we frame the very question we ask of the evidence. When we prefer to believe something, we may approach the relevant evidence by asking ourselves, “what evidence is there to support this belief?” If we prefer to believe that a political assassination was not the work of a lone gunman, we may ask ourselves about the evidence that supports a conspiracy theory. Note that this question is not unbiased: It directs our attention to supportive evidence and away from information that might contradict the desired conclusion. Because it is almost always possible to uncover some supportive evidence, the asymmetrical way we frame the question makes us overly likely to become convinced of what we hope to be true.

kind of information they consider, but also the amount they examine. When the initial evidence supports our preferences, we are generally satisfied and terminate our search; when the initial evidence is hostile, however, we often dig deeper, hoping to find more comforting information, or to uncover reasons to believe that the original evidence was flawed. By taking advantage of “optional stopping” in this way, we dramatically increase our chances of finding satisfactory support for what we wish to be true.

For desired conclusions, in other words, it is as if we ask ourselves, “Can I believe this?”, but for unpalatable conclusions we ask, “Must I believe this?” The evidence required for affirmative answers to these two questions are enormously different. By framing the question in such ways, however, we can often believe what we prefer to believe, and satisfy ourselves that we have an objective basis for doing so.

First, we are quite possessive and protective of our beliefs, as we are of our material possessions. When someone challenges our beliefs, it is as if someone criticized our possessions.