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March 14 was a standard Saturday night for the weekend before St. Patrick’s Day: “Just a bunch of random people smashing Guinness,” said Andrew, a bartender who works at an “Irish-adjacent” bar in Washington, D.C. From 6 p.m. until last call at 2:30 a.m., Andrew witnessed hundreds of patrons—many of them just over 21—stream in, social distancing be damned. “They were out, and they didn’t really care,” he told me.

As the coronavirus pandemic has spread in the United States, public-health experts have lately been urging people—especially young people, many of whom may not show symptoms, and spread the virus unknowingly—to limit their physical contacts with others, but Andrew described a raucous scene that seems out of step with this moment of worldwide panic and caution. “They knew what was going on and they didn’t care—they were going to keep hugging and high-fiving,” he said. “Personally, I probably was in contact with, like, a thousand people over Friday and Saturday night, and I can only wash my hands so many times.” (Andrew asked to have his last name and the name of his workplace omitted from this article, so that he wouldn’t suffer any negative repercussions.)

Other parts of the city were just as lively this past weekend. The regional magazine Washingtonian cataloged the crowds and long lines at a German beer bar, a cupcake shop, and upscale restaurants, among other establishments. Other media outlets and social-media posts documented the masses that showed up to bars in Los Angeles, Nashville, New Orleans, Chicago, and Boston. Even in Seattle, an epicenter of the outbreak, some bars have been packed.

Some people who carried on with their nonessential weekend outings shared their rationale with reporters. One 40-year-old who went with a friend to their favorite bar on Sunday explained to the Los Angeles Times, “This could be the last bar we go to in a long time.” In Boston, a man in line at a bar with an hour-long wait reasoned to a Boston Globe reporter that, as a pharmacist, he was already going to have a high risk of exposure at work anyway, so “there’s only so much I can do” to avoid the virus. And one compassionate, though still risk-taking, D.C. diner told Washingtonian, “As long as businesses are open and the condition doesn’t worsen, I want to support those folks depending on patrons to make their living.”

These are all understandable human reactions to an overwhelming, highly uncertain crisis. But they are also extremely weak justifications for a choice that ultimately puts one’s short-term social enjoyment ahead of the health—and maybe even lives—of countless people who are more vulnerable to the disease. Beyond lacking clear and forceful guidance from President Trump and his administration, why might people have failed to apprehend the gravity of the outbreak and the importance of staying in?

Baruch Fischhoff, a professor at Carnegie Mellon University who studies human judgment and decision making, had a handful of potential answers. First: “There are very few reported cases in most places, so maybe people [think], ‘This is still not here yet,’” he said. “If you haven’t been following the fact that we haven’t been testing [very much], you might not realize how deceiving the reported cases are.” He mentioned research suggesting that the human brain is well adapted to recording how often specific numbers are reported, but not as well adapted to understanding when those numbers might not be representative of reality.

Second, and relatedly, Fischhoff said, people tend to underestimate the speed at which exponential processes—such as a disease outbreak—unfold. “You really can’t trust your intuitions,” he said. “For anybody—whether it’s politicians or business leaders, or whoever—who’s been seeing the problem growing and relying on their intuitive feeling for how fast it’s going to grow, they’re going to be in trouble.”

For example, in the U.S., the number of confirmed cases of COVID-19, the disease caused by the coronavirus, was 213 on March 9, according to the World Health Organization. On Sunday, six days later, it was 1,678. Over the same period, the number of confirmed cases in France rose from 1,116 to 4,469, and the number in Italy rose from 7,375 to 21,157—and Italy had only 1,689 cases as of March 2. The human brain can have trouble keeping pace with such rapid growth (and a lack of widespread testing means the actual number of Americans with the disease is probably much higher than 1,678 anyway).

Also, Fischhoff guessed, people who do go out probably overrate their own control over whether they get sick. “One of the ways that we exaggerate [our own power] is not realizing how often we touch our face … and how many other people touch the things that we touch,” he said.

He also wondered whether people ignoring recommendations to socially distance were just taking cues from others, including people in positions of authority. For instance, Devin Nunes, a Republican representative from California, said Sunday on Fox News, “One of the things you can do is, if you’re healthy, you and your family, it’s a great time to just go out, go to a local restaurant.” (His logic was that people should support local businesses and service workers.) People can be especially open to recommendations like this if they perceive their values to be in line with the recommender’s, Fischhoff said.

If the revelers weren’t modeling their nonchalance on the comments of those in power, their decision to go out might have been influenced by their friends. “In ambiguous situations, people look for social cues from others,” Fischhoff said. “You say, ‘Well, if other people are doing it, maybe they know something about whether this is an acceptable risk.’” (One D.C. resident reflected on his weekend visits to a restaurant and a bar: “I didn’t plan on going out originally, but most of my friends were, so I went along.”)

Fischhoff did note, however, that the way people make decisions doesn’t vary much from ages 15 to 75, so it’s not that young people are more likely to succumb to a particular cognitive bias or fallacy. What does vary is what people have seen over the course of their life. “People who have had the experience of visiting or taking care of elderly parents or grandparents in nursing homes, or dealt with hospitalizations in their family, probably have learned something about disease transfer,” he said. And a 21-year-old is much less likely than a 61-year-old to have had that sort of experience.

Whatever precise mix of cognitive biases propelled hordes of people to America’s bars and restaurants over the weekend, the fun is now over for many: On Sunday and Monday, local and state governments in Los Angeles, Boston, D.C., and New York announced they’d be restricting restaurants and bars to takeout and delivery only. (In L.A., bars were ordered to close entirely.)

“I’m a full-time bartender, and I’m glad that they’re closing,” Andrew, from D.C., told me. “It needed to happen—it was kind of irresponsible to keep providing people with a platform to congregate like that.” Now, to stop people from going to house parties.

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