“Where does the power come from to see the race to its end?” asks the Scottish sprinter Eric Liddell in a scene from Chariots of Fire. His answer—“from within”—was until recently about as far as we’d come in understanding the roots of dogged persistence.

Besides the famous “marshmallow test,” in which preschoolers who abstain from eating one get rewarded with two, measures of motivation have remained mushy. For most of its existence, even the United States Military Academy at West Point, where the celebration of unflagging commitment is etched into the campus statuary, lacked a reliable determinant of which cadets would have the drive to endure their first seven weeks (colloquially known as “Beast Barracks”) and which would say no más and go home. SAT scores, it turned out, were no predictor, nor were ACT scores, high-school rank, physical fitness, “leadership potential,” or any other measure of aptitude. At one point, military psychologists even showed cadets flash cards of random images in hopes of unearthing some subconscious basis for staying power. That, too, failed.

What finally did work was appallingly simple. In 2004, on their second day at West Point, 1,218 new cadets sat down with a sheet of 12 statements—“I finish whatever I begin,” “setbacks don’t discourage me,” and “new ideas and projects sometimes distract me from previous ones” among them—that they rated on a scale from “not at all like me” to “very much like me.” Drawn up by Angela Duckworth, then a doctoral student and now a psychology professor at the University of Pennsylvania, the test was a cinch compared with those to come. But it successfully predicted who would be there at the end of the seven weeks. The 71 cadets who called it quits tested as well as their peers on everything but Duckworth’s “Grit Scale.”

If you have recently bumped into that word, grit, Duckworth is the reason. She has argued that grit can be developed—and is at least as important as IQ in predicting educational success. In education and parenting circles, her research has provided a much needed antipode to hovering, by which children are systematically deprived of the opportunity to experience setbacks, much less overcome them.

But what does Duckworth’s research suggest for grown-ups, in a professional context? Quite a lot, Duckworth would say. In her forthcoming first book, straightforwardly titled Grit, Duckworth pushes into the world of careers. She argues that grit—perseverance plus the exclusive pursuit of a single passion—is a severely underrated component of career success, and that grown-ups, too, need a better understanding of the nature and prevalence of setbacks.

The ascent of Duckworth’s buzzword owes a lot to her prior doubts about her own grittiness. Clearly, she had talent—a characteristic that Duckworth defines as “how quickly your skills improve when you invest effort.” It’s what enabled her, in her 20s, to hopscotch from one station in the meritocracy to another: Marshall Scholar at Oxford (where she picked up a neuroscience degree), speechwriting intern at the White House, management consultant at McKinsey, and finally science teacher at a charter school. But at age 32, she told me recently, stricken by the thought that she was a dilettante—a promising beginner who always would be one—she enrolled in the doctoral program at Penn, and made a vow not to look sideways for 10 years. Then she set about solving a puzzle that had vexed her during her teaching days: how to get kids to persevere just a little longer in tackling problems that exceeded their current skill set.

Initially, Duckworth guessed that the answer had to do with short-term impulse control. The preschoolers who had held out for that extra marshmallow, after all, ended up as higher academic achievers than the kids who ate the first one. But impulse control did not fully account for how long people persisted at something in the absence of positive feedback such as success. So Duckworth simply began interviewing accomplished people in various fields—sales, publishing, entertainment—and parsing their descriptions of how top performers operated.

What distinguished high performers, she found, was largely how they processed feelings of frustration, disappointment, or even boredom. Whereas others took these as signals to cut their losses and turn to some easier task, high performers did not—as if they had been conditioned to believe that struggle was not a signal for alarm.

To Duckworth, here was an opening. If you could change people’s beliefs about how success happens, then you had a crack at changing their behavior—delaying their quitting point a crucial modicum or two.

But beliefs are themselves gritty and persistent. Duckworth cites surveys supporting this point. Ask Americans which they think is more important to success, effort or talent, and they pick effort two to one. Ask them which quality they’d desire most in a new employee, and they pick industriousness over intelligence five to one. But deep down, they hold the opposite view.

We know this thanks to another researcher, whose work Duckworth draws on, Chia-Jung Tsay of University College London. Tsay asked professional musicians to listen to audio clips of two pianists, one described as a “natural,” the other as a “striver.” Despite the fact that the two pianists were really one pianist playing different sections of the same composition—and in flat contradiction to the listeners’ stated belief that effort trumped talent—the musicians thought the “natural” sounded more likely to succeed than the “striver,” and more hirable. Tsay found a similar prejudice among people considering an investment proposal. Their preference for backing a “natural” entrepreneur over a “striver” entrepreneur was erased only when the latter was given four more years of experience and $40,000 more in capital.

Whence the bias for naturals? Duck-worth offered me her best guess: We don’t like strivers because they invite self-comparisons. If what separates, say, Roger Federer from you and me is nothing but the number of hours spent at “deliberate practice”—as the most-extreme behavioralists argue—our enjoyment of the U.S. Open could be interrupted by the thought There but for the grace of grit go I.

Whatever its origins, the bias has practical implications. Certainly, it suggests that my deep terror of letting anyone see my half-written article drafts is not irrational but adaptive. It perpetuates a myth that I’m a natural—the words just flow out, folks, as fast as I can type!—and hides the far more mundane truth: that the words come out fitfully and woodenly, gradually succumbing to a state of readability only after many seemingly fruitless sessions. “If people knew how hard I had to work to gain my mastery, it would not seem so wonderful at all,” Michelangelo observed. Nietzsche concurred: “Wherever one can see the act of becoming one grows somewhat cool.”

Which suggests that Duckworth’s basic admonition, “Embrace challenge,” needs a qualifier: Do it in private. Grit may be essential. But it is not attractive.

This can make for confusing career advice. “Try hard enough and you can do just about anything, as long as you don’t seem to be trying very hard” is not the stuff of school murals. Yet the combination of private toil and public ease, Duckworth agreed, may well be the beau idéal between countervailing imperatives.

Still, the prevalence of hidden practice among successful people is costly to society because it obscures the amount of failure that goes into success. Go on YouTube, Duckworth suggests in her book, and try to find footage of “effortful, mistake-ridden, repetitive deliberate practice.” I did, and took her point. You cannot watch Yo-Yo Ma tediously repeating a difficult passage, or Ronald Reagan practicing his speeches in front of a mirror, or Steve Jobs unveiling a half-baked iPhone. (The closest I came was the discovery of an early Rolling Stones draft of “Start Me Up.” Suffice it to say: The song does not work as a reggae tune.) You see only the final products. If we routinely fool others, they routinely fool us. So when we experience messy frustration, we too readily believe that we don’t have the right stuff and give up.

As a direct countermeasure, Duckworth told me, she started changing her interactions with the dozen young researchers who work in her lab. They needed to see the rejection letters she received from peer-reviewed publications, she decided, and so she started circulating each one as it came in: pages upon pages of sometimes savage attacks of the sort professors regularly deal one another, anonymously, by way of saying an article is unfit for publication. This is not something she would have done, Duckworth quickly noted, at a less secure moment in her career. But getting a MacArthur genius grant (as Duckworth did, in 2013) allows you to, among other things, hold your failure up to others and say, in effect, this is what success looks like.

Duckworth’s book is at its best when it, too, is showing the mess behind success. What she proves, scientifically, is limited. Of the various groupings where she finds the Grit Scale to predict staying power—Green Beret candidates, National Spelling Bee contestants, Chicago public-school students—only a couple (Teach for America participants and salespeople at a vacation-time-share company) involve a workforce. But what sticks with you are the testimonials, collected from sources as disparate as Will Smith, William James, and Jeff Bezos’s mom, that relentlessly deflate the myth of the natural.

If I was left with one nagging question after reading Duckworth’s book, it had to do with the second part of her grit recipe. Just half of the Grit Scale’s questions are designed to measure perseverance, or the determination to meet a particular challenge. The other half measure what she calls passion but might be better understood as directional consistency, or the ability to stick unswervingly to a single, superordinate goal over a period of years. Duckworth mentions a journalist who chose his path precisely because “the journalism industry was very hierarchical, and it was clear how to get from A to B to C to D.” But that describes journalism maybe 15 years ago. Which made me wonder: How well does this approach—basically, pick one long-range goal, keep your head down, and don’t take a step sideways—hold up in an economy where career paths can twist and even vanish with little warning? Shouldn’t you keep your head up, ready for the next pivot? Or have many irons in the fire, as the champions of “career agility” suggest?

Duckworth gamely admitted to me that she had not thought of this—a result, perhaps, of her roots in education (where the paths to success have clear signposts) and her position in academia, one of the last truly guild-like domains. “Grit may carry risk,” she thought out loud, “because it’s about putting all your eggs in one basket, to some extent.”

Even if Grit’s career advice is partly outmoded—or applicable only to fields where the rules of advancement remain stable—it may be useful, anyway, to the extent that we need some direction to get anywhere. And if we are forced to switch paths? Well, that requires grit too. I thought of Intel’s Andy Grove, a chemical engineer who, at age 32, suddenly found himself in charge of a chip-fabrication plant full of people he was supposed to manage. A more complacent person might have lunged for the comfort of his existing skill set. But Grove opened a school notebook and posed himself the question What is a manager?

He pasted in news clippings (Time’s description of a movie director’s role, for instance), annotated these with more questions (“My job description?”), and began to bear down on his fuzzy new understandings by sketching them as graphs. It’s the record of a man repeatedly hurling himself against an unfamiliar challenge. In the end, the notebook was full.