While critics are overly-aware of the president’s lies, a little-known psychological quirk can help explain why Donald Trump’s supporters are so sure of him — and why they can’t see that he’s full of it.

Ex-Obama administration aide Cass Sunstein noted in a Bloomberg op-ed published Thursday that the field of heuristics, or mental shortcuts, helps us establish rules of thumb when we don’t have hard proof.

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“In deciding whether a product or activity is risky, people tend to ask: Do I know about situations in which someone actually got hurt?” he wrote. “That’s the ‘availability heuristic’ in action.”

The “confidence heuristic” is one of the lesser-known types of these mental shortcuts, primarily because it was theorized in the mid-1990’s.

“When we are listening to others,” Sunstein wrote, “we are more likely to be persuaded by people who seem really confident.”

Research shows that people are most likely to follow “the views of their most confident member,” who is likely to be considered more credible. People being proven wrong can hurt this confidence quotient, but in the case of Trump, there is an entire system in place to sow doubt — his constant cries of “fake news.”

“Philip Tetlock of the University of Pennsylvania has found that most people respond more enthusiastically to simple, clear rhetoric from leaders,” the legal scholar wrote, “downplaying tradeoffs, than to complex rhetoric that points to competing considerations and that can easily be seen as a sign of weakness.”

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Trump is far from the first politician to exhibit the confidence heuristic, Sunstein added. Presidents John F. Kennedy and Ronald Reagan were experts at it as well.

“But President Trump outdoes Reagan – not through wit, humor or charm, but through a kind of joyful, thuggish certainty about his own amazingness,” the writer noted. “’I alone can fix it,’ he said during the campaign. ‘Nobody’s ever done a better job than I’m doing as president,’ he says now.”

While the president’s “braggadocio” is a turn-off for many, it has an adverse effect on his supporters, making it “appealing and even contagious.”

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“For people who aren’t sure whether to support him, it can be highly effective,” Sunstein wrote. “Many voters think: If he’s so sure of himself, he’s probably right.”