In a career spent studying ballet dancers, surgeons, spelling bee champions, professional violinists and Shakespearean actors, K. Anders Ericsson reached a conclusion that surprised fellow scientists and left self-help gurus nodding in agreement.

Dr. Ericsson, a Swedish-born cognitive psychologist, found that expertise was the result not of natural talent but of hard work — “deliberate practice,” as he put it, that distinguished the most exceptional performers, artists and athletes from the very good and the halfway decent.

“Consistently and overwhelmingly, the evidence showed that experts are always made, not born,” he once wrote, explaining that when it came to the development of experts and other masters of their craft, nature took a back seat to nurture.

Dr. Ericsson, one of the world’s preeminent experts on experts, was 72 when he died June 17 at his home in Tallahassee. A longtime professor at Florida State University, he wrote widely cited articles and books in addition to offering advice to coaches, executives and organizations such as the Philadelphia Eagles, Cirque de Soleil, Google and the CIA.

“I think of Anders as demystifying excellence,” said Angela Duckworth, a psychology professor at the University of Pennsylvania who co-wrote a 2010 article with Dr. Ericsson on deliberate practice and the National Spelling Bee. In a telephone interview, she linked his work to a debate that 19th-century philosopher Friedrich Nietzsche had with composer Richard Wagner over the nature of genius.

“Nietzsche said that genius seems to be something qualitatively different than what anyone else can do, but it’s not,” she said. “And I think we had to wait a couple centuries for Anders to put this stuff under the microscope scientifically. What Anders was able to do was show that Nietzsche was right” — that excellence “is human, not superhuman.”

Dr. Ericsson reached an increasingly broad audience after Malcolm Gladwell drew on his research for the best-selling book “Outliers” (2008), which popularized the “10,000-hour rule” for the amount of time it takes to master a given field. Citing examples including the Beatles, who honed their sound through grueling all-night concerts in Hamburg, Gladwell wrote that 10,000 hours was “the magic number of greatness.”

But there was nothing “magical” about that figure, said Dr. Ericsson, who had co-written a 1993 study finding that top performers at a German music academy practiced for an average of 10,000 hours by age 20. “The point that we were trying to make,” he told Psych Report magazine in 2016, “was that even the most talented individuals, in order to reach the highest levels, spent tremendous amounts of time working and practicing by themselves.”

Crucially, Dr. Ericsson argued that the way a person practiced mattered just as much, if not more, than the amount of time they committed to their craft. Deliberate practice occurred “at the edge of one’s comfort zone” and involved setting specific goals, focusing on technique and obtaining immediate feedback from a teacher or mentor.

“He really stressed that usually, deliberate practice is very onerous,” said his wife, fellow Florida State psychologist Natalie Sachs-Ericsson. “It’s not fun. If you’re having fun playing your musical instrument, that’s great, but it’s really the times when you’re struggling and working consistently to push yourself further that you get better.”

Dr. Ericsson often noted that while deliberate practice was key, height and body size were rare genetic traits that made a difference, at least when it came to fields like professional basketball and gymnastics. But he said he couldn’t verify any other traits that might account for variations in achievement — fueling criticism from psychologists who argued that other factors, such as natural differences in mental ability, play a role in developing expertise.

Some recent papers, including a 2014 report compiling results from 88 studies, found that practice time accounted for some but not all differences in performance. “We found that, yes, practice is important, and of course it’s absolutely necessary to achieve expertise,” co-author Zach Hambrick, a psychologist at Michigan State University, told the New York Times in 2014. “But it’s not as important as many people have been saying.”

Dr. Ericsson was unswayed, arguing that such studies conflated total practice time with the intense, deliberate practice that he described as crucial to success. “I’ve been spending now 30 years trying to look for kind of limits that would actually constrain some individuals from being successful in some domain,” he told Business Insider in 2016. “And I’m surprised that I’ve yet really to find such limits.”

Karl Anders Ericsson was born in Stockholm on Oct. 23, 1947. The oldest of three children, he went by Anders (preferring the Swedish pronunciation, “on-dish”) and initially studied nuclear engineering, following a similar career path as his father, a civil engineer.

But he soon turned toward psychology and received a bachelor’s degree from the University of Stockholm about 1969, when he married a psychology classmate, Anna-Lena Malm. They both pursued PhDs at the university, where Malm recalled that Dr. Ericsson “was not shy” about contacting luminaries in the field.

On a whim, she said, he sent his doctoral thesis to the American polymath Herbert A. Simon, a future winner of the Nobel Prize in economics, and invited Simon to Stockholm to publicly debate his thesis — a final step toward receiving a PhD.

Simon obliged and then issued an invitation of his own, offering Dr. Ericsson a postdoctoral fellowship at Carnegie Mellon University in Pittsburgh.

Dr. Ericsson, who received his doctorate in 1976, conducted his early research on “think-aloud protocols,” in which subjects were invited to think aloud as they solved an 8-puzzle, a kind of two-dimensional Rubik’s Cube. Collaborating with Simon, he later oversaw memory experiments in which he trained subjects to recite an increasingly long strain of random numbers, suggesting that memory is not a natural talent but a learned skill.

“With the first subject, after about 20 hours of training, his digit span had risen from 7 to 20,” Dr. Ericsson told the Times in 2006. “He kept improving, and after about 200 hours of training he had risen to over 80 numbers.”

The key, he found, was learning to associate meaning with the numbers, often by breaking down a long string of digits into digestible chunks of two or three, with each chunk associated with a telephone number, a long-distance running time or other meaningful bit of information.

Dr. Ericsson soon moved from issues of memory to expertise in general and taught at the University of Colorado Boulder before joining Florida State in Tallahassee in 1992. He co-edited “The Cambridge Handbook of Expertise and Expert Performance” (2006), one of the first textbooks on expertise studies, and recently co-wrote “Peak: Secrets From the New Science of Expertise” (2016) with Robert Pool.

“Anders was the consummate scholar,” his Florida State colleague Neil H. Charness wrote in a tribute. “He wrote papers of the very highest quality, carefully researching issues. Unlike the bite-size snacks that much of our literature is composed of today, when you sit down to read his work, it is like being at a banquet.”

Dr. Ericsson’s first marriage ended in divorce, and in 1985 he married Sachs-Ericsson, who confirmed his death and said the cause was believed to be a cardiac event or a blood clot.

In addition to his wife, of Tallahassee, survivors include two children from his first marriage, Lina and Jens Ericsson, both of San Diego; a sister; a brother; and a grandson.

While Dr. Ericsson often turned to sports for his research, he was not much of an athlete himself, according to his wife, preferring to bury himself in books that filled his house and obscured his office desk. During the coronavirus pandemic, he passed the time at home roaming through Google Scholar, looking for new information about various subjects.

“That is sort of like play for me,” he told the Times in April. Developing a new skill or area of intellectual expertise, he added, could serve as a coping mechanism of sorts, as when concentration camp prisoners “developed impressive skills at mental multiplication” during World War II.

“Once you acquire a skill, there are activities you can do that are much more enjoyable,” he said. “Once you experience what changes you can accomplish, that changes your perception of what’s possible, it changes your mind about what’s possible.”

Correction: An earlier version of this obituary incorrectly reported the year Anders Ericsson received his doctorate. It was 1976, not 1969.