Professional deciders, Johnson reports, use decision processes to navigate this complexity. Many of the best processes unfold in stages—a divergence stage might precede a convergence stage—and are undertaken by groups. (Darwin might have divided his friends into two opposing teams, in the divergence stage, and then held a debate between them.) The decision might be turned into an iterative adventure. In a series of meetings known as a “design charrette”—the concept is borrowed from the field of product design—a large problem is divided into subproblems, each of which is assigned to a group; the groups then present their work to the whole team, receive feedback, regroup, and revise, in a cycle that loops until a decision has been made. (For architects in nineteenth-century Paris, working en charrette meant revising until the very last minute, even in the cart on the way to deliver a design to a panel of judges.) Charrettes are useful not just because they break up the work but because they force groups with different priorities and sensibilities—coders and designers, architects and real-estate developers—to interact, broadening the range of available viewpoints.

At firms like Royal Dutch Shell, where growth requires investing in expensive ventures, such as ports, wells, and pipelines, deciders use “scenario planning” to imagine how such investments might play out. (A scenario-planning starter kit, Johnson writes, contains three possible futures: “You build one model where things get better, one where they get worse, and one where they get weird.”) Military planners use immersive war games, carried out in the field or around a table, to bring more of the “decision map” into view. In such games, our enemies discover possibilities that we can’t foresee, ameliorating the poverty of our individual imaginations. And since the games can be played over and over, they allow decision-makers to “rewind the tape,” exploring many branches of the “decision tree.”

It would be strange to stage a war game about a prospective marriage. Still, Johnson writes, decision science has lessons for us as individuals. Late in “Farsighted,” he recounts his own use of decision-scientific strategies to persuade his wife to move, with their two children, from New York City to the Bay Area. Johnson starts with intuitions—redwoods are beautiful; the tech scene is cool—but quickly moves beyond them. He conducts a “full-spectrum analysis,” arriving at various conclusions about what moving might mean financially, psychologically (will moving to a new city make him feel younger?), and existentially (will he want to have been “the kind of person who lived in one place for most of his adult life”?). Johnson summarizes his findings in a PowerPoint deck, then shows it to his wife, who raises objections that he hasn’t foreseen (all her friends live in Brooklyn). Eventually, they make a contract. They’ll move, but if after two years she wants to return to New York they’ll do so, “no questions asked”—a rewind.

Seven years later, they’re happy with a bicoastal existence. Would Johnson have benefitted from “conducting a multidisciplinary charrette” to explore his family’s move? Probably not. Still, he writes, the principles of decision science—“seeking out diverse perspectives on the choice, challenging your assumptions, making an explicit effort to map the variables”—constituted “a step up” from the pro-and-con lists that Franklin and Darwin would have made. Looking back on his decision, Johnson can at least feel confident that he made one.

Johnson’s book is part of a long tradition. For centuries, philosophers have tried to understand how we make decisions and, by extension, what makes any given decision sound or unsound, rational or irrational. “Decision theory,” the destination on which they’ve converged, has tended to hold that sound decisions flow from values. Faced with a choice—should we major in economics or in art history?—we first ask ourselves what we value, then seek to maximize that value.