In the early seventies, as an assistant professor at Oberlin College, Clance kept hearing female students confessing experiences that reminded her of her own: they were sure they’d failed exams, even if they always did well; they were convinced that they’d been admitted because there had been an error on their test scores or that they’d fooled authority figures into thinking they were smarter than they actually were. Clance began comparing notes with one of her colleagues, Suzanne Imes, about their shared feelings of fraudulence. Imes had grown up in Abilene, Texas, with an older sister who early on had been deemed “the smart one”; as a high schooler, Imes had confessed anxieties to her mother that sounded exactly like the ones Clance had to hers. Imes particularly remembered crying after a Latin test, telling her mother, “I know I failed” (among other things, she’d forgotten the word for “farmer”). When it turned out that she’d got an A, her mother said, “I never want to hear about this again.” But her accomplishment didn’t make the feelings go away; it only made her stop talking about them. Until she met Clance.

One evening, they threw a party for some of the Oberlin students, complete with strobe lights and dancing. But the students looked disappointed and said, “We thought we were going to be learning something.” They were hypervigilant, so intent on staving off the possibility of failure that they couldn’t let loose for even a night. So Clance and Imes turned the party into a class, setting up a circle of chairs and encouraging the students to talk. After some of them confessed that they felt like “impostors” among their brilliant classmates, Clance and Imes started referring to the feelings they were observing as “the impostor phenomenon.”

The pair spent five years talking to more than a hundred and fifty “successful” women: students and faculty members at several universities; professionals in fields including law, nursing, and social work. Then they recorded their findings in a paper, “The Impostor Phenomenon in High Achieving Women: Dynamics and Therapeutic Intervention.” They wrote that women in their sample were particularly prone to “an internal experience of intellectual phoniness,” living in perpetual fear that “some significant person will discover that they are indeed intellectual impostors.” But it was precisely this process of discovery that helped Clance and Imes formulate the concept—as they recognized feelings in each other, and in their students, that they’d been experiencing all their lives.

At first, the paper kept getting rejected. “Weirdly, we didn’t get impostor feelings about that,” Clance told me, when I visited her at her home, in Atlanta. “We believed in what we were trying to say.” It was eventually published in 1978, in the journal Psychotherapy: Theory, Research, and Practice. The paper spread like an underground zine. People kept writing to Clance to ask for copies, and she sent out so many that the person working the copy machine in her department asked, “What are you doing with all these?” For decades, Clance and Imes saw their concept steadily gaining traction—in 1985, Clance published a book, “The Impostor Phenomenon,” and also released an official “I.P. scale” for researchers to license for use in their own studies—but it wasn’t until the rise of social media that the idea, by now rebranded as “impostor syndrome,” truly exploded.

Almost fifty years after its formulation, the concept has achieved a level of cultural saturation that Clance and Imes never imagined. Clance maintains a list of studies and articles that have referenced their original idea; it is now more than two hundred pages long. The concept has inspired a micro-industry of self-help books, ranging in tone from #girlboss self-empowered sass (“The Middle Finger Project: Trash Your Imposter Syndrome and Live the Unf*ckwithable Life You Deserve”) to unapologetic earnestness (“Yes! You Are Good Enough: End Imposter Syndrome, Overthinking and Perfectionism and Do What YOU Want”). “The Imposter Syndrome Workbook” invites readers to draw their impostor voice as a creature or a monster of their choosing, to cross-examine their negative self-talk, and to fill a “Self-Love Mason Jar” with written affirmations and accomplishments.

The phrase “impostor syndrome” often elicits a fierce sense of identification, especially from millennial and Gen X women. When I put out a call on Twitter for experiences of impostor syndrome, I was flooded with responses. “Do you have room in your inbox for roughly 180,000 words?” a high-level publishing executive wrote. A graduate of Trinity College Dublin confessed that her feelings of fraudulence were so strong that she’d been unable to enter the college’s library for her entire first year. A university administrator said, “I grew up on a pig farm in rural Illinois. Whenever I attend a fancy event, even if it is one I am producing, I feel like people will still see hayseed in my hair.” An artisanal-cider maker wrote, “I’ve made endless ciders, but each and every time that I start fermenting, my mind goes, ‘This is the one when everyone will find out you don’t know what you’re doing.’ ”

The eminent are not immune. In fact, Clance and Imes argued forcefully in their original study that success was not a cure. Maya Angelou once said, “I have written eleven books, but each time I think, Uh-oh, they’re going to find out now. I’ve run a game on everybody, and they’re going to find me out.” Neil Gaiman, in a commencement address that went viral, described his fear of being busted by the “fraud police,” whom he imagined showing up at his door with a clipboard to tell him he had no right to live the life he was living. (Although men do report feeling like impostors, the experience is primarily associated with women, and the word “impostor” has been granted special feminized forms—“impostrix,” “impostress”—since the sixteen-hundreds.)

Clance and Imes remain stunned by how broadly their idea has circulated. “We had no idea,” Imes said. “We were just as surprised as everyone else.” But their ambitions were never small. “We saw suffering in a lot of people, and we hoped we could help,” Imes told me. “We wanted to change people’s lives.”