Everything Is Obvious_ _Once You Know the Answer - Duncan J. Watts [61]
For much the same reason, professional historians are often at pains to emphasize the difficulty of generalizing from any one particular context to any other. Nevertheless, because accounts of the past, once constructed, bear such a strong resemblance to the sorts of theories that we construct in science, it is tempting to treat them as if they have the same power of generalization—even for the most careful historians.18 When we try to understand why a particular book became a bestseller, in other words, we are implicitly asking a question about how books in general become bestsellers, and therefore how that experience can be repeated by other authors or publishers. When we investigate the causes of the recent housing bubble or of the terrorist attacks of September 11, we are inevitably also seeking insight that we hope we’ll be able to apply in the future—to improve our national security or the stability of our financial markets. And when we conclude from the surge in Iraq that it caused the subsequent drop in violence, we are invariably tempted to apply the same strategy again, as indeed the current administration has done in Afghanistan. No matter what we say we are doing, in other words, whenever we seek to learn about the past, we are invariably seeking to learn from it as well—an association that is implicit in the words of the philosopher George Santayana: “Those who cannot remember the past are condemned to repeat it.”19
This confusion between stories and theories gets to the heart of the problem with using common sense as a way of understanding the world. In one breath, we speak as if all we’re trying to do is to make sense of something that has already happened. But in the next breath we’re applying the “lesson” that we think we have learned to whatever plan or policy we’re intending to implement in the future. We make this switch between storytelling and theory building so easily and instinctively that most of the time we’re not even aware that we’re doing it. But the switch overlooks that the two are fundamentally different exercises with different objectives and standards of evidence. It should not be surprising then that explanations that were chosen on the basis of their qualities as stories do a poor job of predicting future patterns or trends. Yet that is nonetheless what we use them for. Understanding the limits of what we can explain about the past ought therefore to shed light on what it is that we can predict about the future. And because prediction is so central to planning, policy, strategy, management, marketing, and all the other problems that we will discuss later, it is to prediction that we now turn.
CHAPTER 6
The Dream of Prediction
Humans love to make predictions—whether about the movements of the stars, the gyrations of the stock market, or the upcoming season’s hot color. Pick up the newspaper on any given day and you’ll immediately encounter a mass of predictions—so many, in fact, that you probably don’t even notice them. To illustrate the point, let’s consider a single news story chosen more or less at random from the front page of the New York Times. The story, which was published in the summer of 2009, was about trends in retail sales and contained no fewer than ten predictions about the upcoming back-to-school season. For example, according to one source cited in the article—an industry group called the National Retail Federation—the average family with school-age children was predicted to spend “nearly 8 percent less this year than last,” while according to the