In July of 1838, Charles Darwin was twenty-nine years old and single. Two years earlier, he had returned from his voyage aboard H.M.S. Beagle with the observations that would eventually form the basis of “On the Origin of Species.” In the meantime, he faced a more pressing analytical problem. Darwin was considering proposing to his cousin Emma Wedgwood, but he worried that marriage and children might impede his scientific career. To figure out what to do, he made two lists. “Loss of time,” he wrote on the first. “Perhaps quarreling. . . . Cannot read in the evenings. . . . Anxiety and responsibility. Perhaps my wife won’t like London; then the sentence is banishment and degradation into indolent, idle fool.” On the second, he wrote, “Children (if it Please God). Constant companion (and friend in old age). . . . Home, & someone to take care of house.” He noted that it was “intolerable to think of spending one’s whole life, like a neuter bee, working, working. . . . Only picture to yourself a nice soft wife on a sofa with good fire and books and music perhaps.”

Beneath his lists, Darwin scrawled, “Marry, Marry, Marry QED.” And yet, Steven Johnson writes, in “Farsighted: How We Make the Decisions That Matter the Most,” “we have no evidence of how he actually weighed these competing arguments against each other.” Johnson, the author of “How We Got to Now” and other popular works of intellectual history, can’t help but notice the mediocrity of Darwin’s decision-making process. He points out that Benjamin Franklin used a more advanced pro-and-con technique: in what Franklin called “Prudential Algebra,” a numerical weight is assigned to each listed item, and counterbalancing items are then eliminated. (“If I find a Reason pro equal to some two Reasons con, I strike out the three . . . and thus proceeding I find at length where the Ballance lies,” Franklin explained to a friend.) Even this approach, Johnson writes, is slapdash and dependent upon intuition. “The craft of making farsighted choices—decisions that require long periods of deliberation, decisions whose consequences might last for years,” he concludes, “is a strangely under-appreciated skill.”

We say that we “decide” to get married, to have children, to live in particular cities or embark on particular careers, and in a sense this is true. But how do we actually make those choices? One of the paradoxes of life is that our big decisions are often less calculated than our small ones are. We agonize over what to stream on Netflix, then let TV shows persuade us to move to New York; buying a new laptop may involve weeks of Internet research, but the deliberations behind a life-changing breakup could consist of a few bottles of wine. We’re hardly more advanced than the ancient Persians, who, Herodotus says, made big decisions by discussing them twice: once while drunk, once while sober.

Johnson hopes to reform us. He examines a number of complex decisions with far-reaching consequences—such as the choice, made by President Barack Obama and his advisers, to green-light the raid on Osama bin Laden’s presumed compound, in Abbottabad, Pakistan—and then shows how the people in charge drew upon insights from “decision science,” a research field at the intersection of behavioral economics, psychology, and management. He thinks that we should apply such techniques to our own lives.

I’ve never had to decide whether to launch a covert raid on a suspected terrorist compound, but I’ve made my share of big decisions. This past summer, my wife and I had a baby boy. His existence suggests that, at some point, I decided to become a father. Did I, though? I never practiced any prudential algebra; rather than drawing up lists of pros and cons and concluding, on balance, that having kids was a good idea, I gradually and unintentionally transitioned from not particularly wanting children to wanting them, and from wanting them to joining my wife in having them. If I made a decision, it wasn’t a very decisive one. In “War and Peace,” Tolstoy writes that, while an armchair general may imagine himself “analyzing some campaign on a map” and then issuing orders, a real general never finds himself at “the beginning of some event”; instead, he is perpetually situated in the middle of a series of events, each a link in an endless chain of causation. “Can it be that I allowed Napoleon to get as far as Moscow?” Tolstoy’s General Kutuzov wonders. “When was it decided? Was it yesterday, when I sent Platov the order to retreat, or was it the evening before, when I dozed off and told Bennigsen to give the orders? Or still earlier?” Unlike the capture of Moscow by Napoleon, the birth of my son was a joyous occasion. Still, like Kutuzov, I’m at a loss to explain it: it’s a momentous choice, but I can’t pinpoint the making of it in space or time.

For Tolstoy, the tendency of big decisions to make themselves was one of the great mysteries of existence. It suggested that the stories we tell about our lives are inadequate to their real complexity. Johnson means to offer a way out of the Tolstoyan conundrum. He wants to make us writers, rather than readers, of our own stories. Doing so requires engaging with one of life’s fundamental questions: Are we in charge of the ways we change?

Ideally, we’d be omniscient and clearheaded. In reality, we make decisions in imperfect conditions that prevent us from thinking things through. This, Johnson explains, is the problem of “bounded rationality.” Choices are constrained by earlier choices; facts go undiscovered, ignored, or misunderstood; decision-makers are compromised by groupthink and by their own fallible minds. The most complex decisions harbor “conflicting objectives” and “undiscovered options,” requiring us to predict future possibilities that can be grasped, confusingly, only at “varied levels of uncertainty.” (The likelihood of marital quarrelling must somehow be compared with that of producing a scientific masterwork.) And life’s truly consequential choices, Johnson says, “can’t be understood on a single scale.” Suppose you’re offered two jobs: one at Partners in Health, which brings medical care to the world’s neediest people, and the other at Goldman Sachs. You must consider which option would be most appealing today, later this year, and decades from now; which would be preferable emotionally, financially, and morally; and which is better for you, your family, and society. From this multidimensional matrix, a decision must emerge.

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.