Asked who did what in their collaboration, psychologist Daniel Kahneman replied, “We didn’t know at that time, not clearly. It was beautiful not knowing.” Geniuses often work on their own, Mr. Kahneman added. “I am not a genius. Neither is [Amos] Tversky. Together we are exceptional.”

Indeed, they were. The papers the two psychologists wrote in the 1970s and ’80s demonstrated that human beings err, systemically, when making decisions in uncertain situations. Their insights into human psychology have had a profound impact on law, government regulation, evidence-based medicine and the field of emerging behavioral economics.

In “The Undoing Project: A Friendship That Changed Our Minds,” author Michael Lewis tells the story of the relationship between Amos Tversky and Daniel Kahneman — and unpacks their explanations of the fallibility of human intuition and reason. The author of “Liar’s Poker,” “Moneyball,” “The Big Short” and “Flash Boys,” Mr. Lewis is a master of nonfiction narrative. “The Undoing Project” may well be his best book.

The relationship between Mr. Tversky and Mr. Kahneman, Mr. Lewis implies, lends support to the old saw that opposites attract. To be sure, both men served with distinction in the Israeli army, got their doctorates in psychology, and received prestigious academic appointments. But Mr. Kahneman, a survivor of Nazi-occupied France, was perennially anxious, insecure and skeptical, while Mr. Tversky, a paratrooper and platoon commander, was popular, self-confident and combative. That said, Mr. Lewis indicates, from the moment they met at Hebrew University in Jerusalem, they were lovers, “in every way but sexually.”

Their research, Mr. Lewis demonstrates, demolished the notion that human beings are fundamentally rational. Although choice depends on context, Mr. Tversky and Mr. Kahneman emphasized, decision makers tend to frame it in isolation. Two American college students at the University of Pittsburgh might conclude that they have nothing in common with one another; on a junior year abroad in Togo they might become friends. And by framing “choice architecture” differently (for example, by requiring workers to opt out of rather than into a retirement savings account), policy makers can stimulate significant changes in behavior.

According to Mr. Kahneman and Mr. Tversky (they alternated lead authorship on their publications), most of us tend to fall back on stereotypes (Jeremy Lin doesn’t match our mental picture of a stellar professional basketball player) — or on a fact or incident we have recently learned or experienced — when asked to evaluate anything with a random component. Most people have a greater aversion to a loss than an appetite for gain. And we fall prey to “hindsight bias,” taking observed facts and fitting them neatly into a pattern that “explains” an outcome, and berating ourselves (and others) for failing to foresee “the inevitable.”

Perhaps inevitably, the extraordinary and improbable collaboration of Mr. Kahneman and Mr. Tversky ended. The relationship, Mr. Lewis tells us, was strained by Mr. Kahneman’s view that Mr. Tversky (the sole recipient of a MacArthur genius grant) was receiving a disproportionate amount of credit for their work and appeared quite “willing to accept a situation that put me in his shadow.” Poignantly, the collaboration came apart while the pair was working on “an undoing project”: an examination of the tendency of human beings to create “alternative versions of reality” to “undo” experiences that lead to regret, sorrow or frustration.

By the mid-’80s, Mr. Lewis writes, Mr. Tversky and Mr. Kahneman were “like a pair of swimmers caught in different currents, losing the energy to swim against them.” They separated — and, in essence, divorced.

Within days of Mr. Kahneman’s declaration that they were no longer friends, however, doctors told Mr. Tversky he had a malignant melanoma. The two talked nearly every day. Danny suggested that they write something together, but Amos died before they could finish. Their work, Michael Lewis implies, will never be undone.

Glenn C. Altschuler is the Thomas and Dorothy Litwin Professor of American Studies at Cornell University.

First Published: January 15, 2017, 5:00 a.m.