I’m an emergency room doctor in Boston. I can’t help but feel like Cassandra these days. A Trojan royal, Cassandra was cursed by Apollo after she rebuffed his advances – she could see into the future, but no one would ever believe what she saw.

Last Friday, I told my father that he shouldn’t return to his office after the weekend, due to the rapid, unmitigated spread of the coronavirus.

“Why not?” he said. “I’m healthy.”

He is generally healthy, but I pointed out that he’s almost in an age group that, in Wuhan, had a one in 10 chance of dying from the virus.

I asked my younger brother, a college student, what he thought about the virus.

“Think it’s getting blown way out of proportion,” he texted back.

That was on 11 March. I can’t imagine what it’s been like for the physicians and scientists who have been warning of a pandemic like this one for decades.

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Things have changed so much in just a few days. In Boston, where I live, restaurants are now takeout only. New York City has shuttered its schools, and San Francisco has advised people to shelter in place. European countries have sealed their borders. Cities are enforcing overnight curfews. Disneyland is closed. My father’s company has moved to remote work, and my younger brother is asking if he should isolate himself in his dorm room to protect our parents, rather than go home.

But naysayers and doubters are still, incredibly, refusing to listen to the nearly unanimous voice of the nation’s health and medical authorities, who are pleading for everything to be canceled or closed that can be, and urging aggressive social distancing to limit the virus’s spread.

On Sunday, friends reported that bars and restaurants in Brooklyn were packed. I heard about raucous St Patrick’s Day parties over the weekend here in Boston. And a popular flower market in London was teeming on Sunday. Polls are bearing this out. An NBC News/Wall Street Journal poll conducted 11-13 March found that 56% of Americans believe that the virus will impact their daily lives in only a small way, or not at all. 49% say they haven’t stopped attending large public gatherings like concerts or movies, and 69% haven’t stopped eating out at restaurants.

Some politicians, pundits, and even governments have also seemed unable to grasp the profound gravity of what could lie ahead of us if we don’t take aggressive action immediately. A few days ago Oklahoma’s governor posted a photograph of himself and his family in a crowded restaurant on Twitter. On Sunday, the California representative Devin Nunes said on television that “it’s a great time” to “go to your local pub”. Fox News has had an outsized role in spreading misinformation, with anchors and guests saying that “now is actually the safest time to fly”, arguing that people are “overreacting” to the virus, and suggesting that the virus is an “impeachment scam”.

The British government also appeared oblivious to the public health threat of unmitigated contagion by adopting an unbelievably ill-advised strategy of abandoning serious containment efforts in favor of “some kind of herd immunity” to temper later surges of infection. Notably, this strategy does nothing to prevent hospitals from being overrun in the first and largest surge. (The British government has since modulated its rhetoric.)

As of this writing, authorities seem finally to be gaining some momentum in making the sort of aggressive decisions that can slow the virus’s spread. My mother texted earlier this week to say that Houston, where she lives, is closing bars and limiting restaurants to takeout. Donald Trump has recommended that all Americans limit gatherings to fewer than 10 people. These are important steps in the right direction, but they still rely to a substantial degree on the choices that individual people will make.

Why is it so difficult for us to appreciate the scale of what an unchecked global pandemic could do? The answer may have something to do with how difficult it is to intuitively understand abstract concepts like exponential growth.

This difficulty has been appreciated since at least 1256, when an Islamic scholar recorded what is known as the wheat and chessboard problem. The problem appears in a parable about the inventor of chess, whose king demands to purchase the new game. The inventor names his price, to be paid in wheat. He suggested that one grain of wheat should be placed on the first square of the chessboard, two grains on the second, and so on, with the sum doubling in this way over 64 squares. The king thinks this a great bargain, and is stunned when his treasurer informs him that the sum would bankrupt the kingdom. The total number of grains comes to 18,446,744,073,709,551,615.

Here’s another example. If you took 30 steps from your front door, with each step twice as large as the last, how far could you get? The answer might surprise you – it’s 26 times the Earth’s circumference. Our inability to appreciate how extraordinarily powerful exponential growth can be has concrete consequences. It’s a major reason why people don’t take their retirement accounts seriously enough, for one. It’s also why people seem to be struggling to understand why every single day matters enormously in limiting the spread of the coronavirus, which follows an exponential growth pattern.

We are already in the midst of exponential growth in the coronavirus outbreak, with every indicator suggesting that the virus is now spreading unchecked within communities across the country.

The good news, though, is that if we act today instead of tomorrow we can prevent a huge number of infections, and a lot of deaths. Time is of the absolute essence here, and it’s individual choices that matter the most. Aggressive social distancing, avoiding all non-essential social contact, avoiding public places like bars, restaurants and movie theaters, and practicing obsessive hand hygiene are all critically important. If you have any cold or flu-like symptoms, assume you have the coronavirus and isolate yourself as strictly as possible until two to three days after all symptoms have resolved. If you develop shortness of breath, chest pain, confusion, or marked weakness, then please see a doctor.

It’s a rare situation when the lives of others are in the hands of regular people everywhere, young and old, rich and poor, no matter your occupation, and no matter where you live. We’re living it right now. Please take it so, so seriously.