In their 1999 paper, published in the Journal of Personality and Social Psychology, David Dunning and Justin Kruger put data to what has been known by philosophers since Socrates, who supposedly said something along the lines of “the only true wisdom is knowing you know nothing.” Charles Darwin followed that up in 1871 with “ignorance more frequently begets confidence than does knowledge.”

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Put simply, incompetent people think they know more than they really do, and they tend to be more boastful about it.

To test Darwin’s theory, the researchers quizzed people on several topics, such as grammar, logical reasoning and humor. After each test, they asked the participants how they thought they did. Specifically, participants were asked how many of the other quiz-takers they beat.

Dunning was shocked by the results, even though it confirmed his hypothesis. Time after time, no matter the subject, the people who did poorly on the tests ranked their competence much higher. On average, test takers who scored as low as the 10th percentile ranked themselves near the 70th percentile. Those least likely to know what they were talking about believed they knew as much as the experts.

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Dunning and Kruger’s results have been replicated in at least a dozen different domains: math skills, wine tasting, chess, medical knowledge among surgeons and firearm safety among hunters.

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During the election and in the months after the presidential inauguration, interest in the Dunning-Kruger effect surged. Google searches for “dunning kruger” peaked in May 2017, according to Google Trends, and has remained high since then. Attention spent on the Dunning-Kruger Effect Wikipedia entry has skyrocketed since late 2015.

There’s also “much more research activity” about the effect right now than immediately after it was published, Dunning said. Typically, interest in a research topic spikes in the five years following a groundbreaking study, then fades.

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“Obviously it has to do with Trump and the various treatments that people have given him,” Dunning said, “So yeah, a lot of it is political. People trying to understand the other side. We have a massive rise in partisanship and it’s become more vicious and extreme, so people are reaching for explanations."

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Even though President Trump’s statements are rife with errors, falsehoods or inaccuracies, he expresses great confidence in his aptitude. He says he does not read extensively because he solves problems “with very little knowledge other than the knowledge I [already] had.” He has said in interviews he doesn’t read lengthy reports because “I already know exactly what it is.”

He has “the best words” and cites his “high levels of intelligence” in rejecting the scientific consensus on climate change. Decades ago, he said he could end the Cold War: “It would take an hour and a half to learn everything there is to learn about missiles,” Trump told The Washington Post’s Lois Romano over dinner in 1984. “I think I know most of it anyway.”

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“Donald Trump has been overestimating his knowledge for decades,” said Brendan Nyhan, a political scientist at the University of Michigan. “It’s not surprising that he would continue that pattern into the White House.”

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Dunning-Kruger “offers an explanation for a kind of hubris,” said Steven Sloman, a cognitive psychologist at Brown University. “The fact is, that’s Trump in a nutshell. He’s a man with zero political skill who has no idea he has zero political skill. And it’s given him extreme confidence.”

Sloman thinks the Dunning-Kruger effect has become popular outside of the research world because it is a simple phenomenon that could apply to all of us. And, he said, people are desperate to understand what’s going on in the world.

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Many people “cannot wrap their minds around the rise of Trump,” Sloman said. “He’s exactly the opposite of everything we value in a politician, and he’s the exact opposite of what we thought Americans valued.” Some of these people are eager to find something scientific to explain him.

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Whether people want to understand “the other side” or they’re just looking for an epithet, the Dunning-Kruger effect works as both, Dunning said, which he believes explains the rise of interest.

The ramifications of the Dunning-Kruger effect are usually harmless. If you’ve ever felt confident answering questions on an exam, only to have the teacher mark them incorrect, you have firsthand experience with Dunning-Kruger.

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On the other end of the spectrum, the effect can be deadly. In 2017, former neurosurgeon Christopher Duntsch was sentenced to life in prison for maiming several patients.

“His performance was pathetic,” one co-surgeon wrote about Duntsch after a botched spinal surgery, according to the Texas Observer. “He was functioning at a first- or second-year neurosurgical resident level but had no apparent insight into how bad his technique was.”

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Dunning says the effect is particularly dangerous when someone with influence or the means to do harm doesn’t have anyone who can speak honestly about their mistakes. He noted several plane crashes that could have been avoided if crew had spoken up to an overconfident pilot.

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“You get into a situation where people can be too deferential to the people in charge,” Dunning explained. “You have to have people around you that are willing to tell you you’re making an error.”

What happens when the incompetent are unwilling to admit they have shortcomings? Are they so confident in their own perceived knowledge that they will reject the very idea of improvement? Not surprisingly (though no less concerning), Dunning’s follow-up research shows the poorest performers are also the least likely to accept criticism or show interest in self improvement.