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If America had taken the threat of coronavirus more seriously, countless deaths could have been prevented. The federal government could have stocked up on masks and testing reagents. The United States could have built field hospitals sooner, as China did, in dense places that were likely to be hardest hit. Officials could have advised people to avoid travel and mass gatherings earlier.

Instead, even as evidence of the coronavirus’s severity mounted, an epidemic of wishful thinking spread among both the American public and policy makers. As the virus roamed freely, Americans partied. In mid-March, Italians shared videos of themselves giving the advice they regretted ignoring early in the course of their country’s outbreak. Now some Americans wish they could similarly issue their past selves—and those of elected officials—a wake-up call. Some of us are asking, Why didn’t we see this coming?

The coronavirus caught the U.S. unprepared and turned into one of the biggest disasters in recent memory for many reasons: basic failures of testing equipment, officials reportedly trying to keep the president happy, a public-health system that has been underfunded for years, and a general lack of knowledge about the novel coronavirus’s behavior. But one easily overlooked reason is the human brain’s basic tendency toward optimism, even when the facts suggest we should be worried.

Of course, experts on infectious disease knew a pandemic would soon strike. In 2018, my colleague Ed Yong wrote that “a new infectious disease has emerged every year for the past 30 years.” A few weeks ago, my colleague Uri Friedman explained how intelligence officials and other experts had been warning, since 2012, of a pandemic that could destroy Americans’ way of life. In 2015, Bill Gates, not exactly a little-known figure, described the threat of an infectious virus in a speech that’s been watched millions of times on YouTube.

Nevertheless, outside the infectious-disease community, Americans and our leaders blithely hoped that the virus would somehow pass us over. Even though intelligence reports alerted the White House to the coronavirus threat as early as November, lockdowns in the U.S. did not begin until March. On January 22, the president said, “We have it totally under control.” Even after the Centers for Disease Control and Prevention warned of outbreaks in the U.S., on March 2, New York City Mayor Bill de Blasio urged New Yorkers to “get out on the town.” On March 5, Surgeon General Jerome Adams told Fox News that the risk of coronavirus “is low to the average American.”

Even I, a health reporter, did not initially realize how quickly the virus would descend on the United States, how severe its toll would be, or what shape the fight against it would take. There’s knowing something will happen, and then there’s understanding how, exactly, it will upend your life. On March 2, I spoke with Helen Chu, an epidemiologist at the University of Washington, and she told me that schools might soon shut their doors and sporting events might be canceled. I doubt it will come to that, I thought. After all, our leaders had assured us as much. Within days, schools were closed and the NBA had suspended its season.

That kind of naive optimism in the face of encroaching disaster is a pitfall of owning a human brain, several experts on the psychology of risk perception told me recently. People have trouble appraising exponentially growing problems, seeing exactly how they themselves might be affected, and understanding the best way to help when disaster arrives. Our brains aren’t designed to anticipate threats such as pandemics, which allows the tiny, brainless pathogens to get the upper hand as we fumble along. The only way to counteract these biases, experts say, is to prepare ahead of time. Which is, alas, something the United States also failed to do.

Perhaps for the good of entrepreneurs, American Idol hopefuls, and buyers of real estate on Miami Beach, humans are remarkably bad at imagining everything that could go wrong in a given situation. “We’re likely to have an excessively rosy outlook on life,” says Hersh Shefrin, a behavioral-finance professor at Santa Clara University.

One reason for this subconscious Pollyannaism is that we don’t use the deliberative part of our brain very much. As the psychologist Daniel Kahneman wrote in Thinking, Fast and Slow, our brain has two modes: A fast, intuitive method that’s driven by feelings, and a more analytic (and evolutionarily more recent) way of thinking that’s driven by data. The intuitive process tends to dominate, says Paul Slovic, a psychology professor at the University of Oregon. “We don’t go around calculating things in a scientific way; we just kind of are guided by our feelings, which are very much influenced by our experiences,” he told me.

This knee-jerk part of our brains mostly takes only past events into consideration, making us “prisoners of our experience,” as Slovic put it. One 1962 study of people living on a flood plain found they were unable to conceive of floods bigger than the largest flood they had ever witnessed. It’s easy to infer that Americans similarly couldn’t fathom a disease worse than other, less deadly outbreaks the U.S. has recently faced, such as Zika and Ebola. Despite our brushes with past plagues, Americans might have struggled to imagine one that would cause more than regional disruption and a couple of weeks’ headlines.

In some cases, experience can be instructive. Shefrin points out that some Asian countries reacted differently than the U.S. to the coronavirus because the region had faced SARS in the past. While these countries were aggressively testing and contact tracing, American policy makers were scrambling to remedy the neglected supply of N95 respirators in the Strategic National Stockpile—never replenished after 2009’s swine-flu outbreak, because officials decided to shift their focus to terrorism.

The “fast” instinct in our minds tends especially to minimize risks that are harder to picture. Abstract dangers, such as invisible diseases, seem less threatening to us than do tangible threats, such as terrorists or tornadoes. Our brain interprets low-probability events as having a practically zero chance of happening, and it’s basically hopeless at contemplating exponential figures—such as, say, the way infections spread through a population. The number of cases starts out small, so our fast, intuitive brain tells us it will stay small forever. This is why that riddle about the pond on which lily pads are doubling in volume every day is so tricky. (If the pond is fully covered with lily pads on day 40, on what day do the lilies cover half the pond? The answer is day 39.) “The thing that’s sinister about the exponential-growth curve is that it leaps up all of a sudden and overwhelms you,” Slovic said. In a piece for Nautilus a few years ago, K. C. Cole implicated this exponent innumeracy in explaining how climate change “was able to creep up on most of us with cat feet.” “The greatest shortcoming of the human race,” the physicist Albert Bartlett once said, “is our inability to understand the exponential function.”

This might explain why, on February 23, with 51 confirmed coronavirus cases in the U.S., President Donald Trump reiterated that the situation was “very much under control.” A month later, the number of cases was more than 44,000. Trump, according to Shefrin, is a very intuitive thinker. “He’s got very strong intuition, and he goes with his instincts,” Shefrin says. The problem, of course, is that our intuition isn’t always right.

By the time a disaster is on our doorstep—when hospitals are filling up in Italy but not yet in the U.S.—our minds wrongly soothe us once again. People have trouble envisioning themselves as the kind of person something bad might happen to. For instance, because elderly people have had the highest fatality rates from COVID-19, some younger Americans might think they themselves are invincible. “If we don’t see ourselves as being the victim of a disease like COVID-19, then we’ll be prone to underestimate the likelihood that we will in fact be such a victim,” Shefrin says.

On top of that failure of imagination, a concept called “motivated reasoning” falsely reassures us that the bad thing we don’t want to happen probably won’t. “If you’re the federal government, and you’re hoping to put together a reelection campaign based on economic prosperity, then the idea of global shutdown is a horrible thing,” says Nathan Novemsky, a marketing professor at Yale. “Things that we are motivated not to believe, we’re very good at not believing.”

When the disease finally arrives, and people start dying, our brains fall into a different snare: The number of people affected is too large to be psychologically meaningful. Slovic has found that when many people are affected by a disaster, a kind of psychological numbing occurs. Though people are capable of feeling deeply for a single victim and her plight, “compassion fade” can set in when a tragedy involves two or more victims. People’s positive feelings about donating to a needy child decline for two needy children. This perhaps helps explain why Americans can round up thousands of dollars to donate to individual sick people’s GoFundMe campaigns, but hesitate to support a universal health-insurance system. Similarly, a disease that is likely to wipe out 60,000 Americans, most of whom are strangers, can seem less dangerous than it really is.

The lessons from these gaps in our collective thinking can be useful in planning for future big, amorphous disasters, such as climate change. That is, if we accept and remedy them. In addition to raising awareness of these psychological pitfalls, experts told me, we should put into place mechanisms and laws that will override humans’ disaster-ignoring biases. Saying that we’ll surely be smarter next time isn’t enough; like the people on the flood plain, we probably won’t imagine that the really big one is coming.

Experts say the United States should commit resources to preparation ahead of time, so that our psychological blind spots don’t undermine us. Furthermore, government leaders can explicitly battle these biases by seeking a diversity of viewpoints to stress-test their opinions. But Trump seems to have done the opposite for months, pushing aside truth-tellers and promoting those who tell him what he wants to hear.

“Government is the tool that we convene to protect us from things that we can’t protect ourselves from as individuals,” says David Ropeik, a risk-perception author and consultant. That only works if the government response isn’t dictated by one individual acting on instinct. Individuals may be myopic, but if we strive to look together, we can more clearly see what’s brewing.

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