A weed is growing in a garden, and it doubles in size every week.

If it takes forty weeks to completely cover the garden, how many weeks does it take to cover half?

If your first instinct was “twenty”, your instinct was wrong. The correct answer is thirty-nine.

This is a question few people get right on the first try, because it requires us to think exponentially. And that’s hard to do.

The coronavirus — and indeed every pandemic we face — is nature’s cruel demonstration of exponential growth. Because the virus’s transmission rate (R0) is a number greater than one, each infection carries a subtle multiplier effect that rapidly compounds with time.

Like the garden weed, cases outside of China are doubling approximately every seven days, and this compounding can lead to shocking results. If that rate continues unabated for a little over two months, today’s cases will have increased by a factor of one thousand.

The math involved in pandemic modelling can be highly counterintuitive, and yet so many of us ultimately fall back on our intuitions to guide our opinions on this difficult topic. This concerns me enormously, because this is one instance where our intuitions are almost certainly flawed.


I played poker professionally for ten years, a living derived from the fact that most amateurs struggle to evaluate risk properly. Some players are far too cautious; others, utterly reckless. And from what I’ve seen so far, the spectrum of response to coronavirus is no different.

There are the over-reactors: doomsayers declaring the end times are here while mindlessly clearing the supermarket shelves. There are also the stubborn under-reactors, wearing their indifference as a badge of honour — and in some cases, even mocking those who choose to follow basic precautionary advice. And then there are those of us in the middle, trying to navigate the fine line of sanity between the two.

The trouble is that this is ultimately a question of odds, and thinking in odds is hard. Our everyday language trains us to be vague: we communicate using words like “probably” and “likely” as though they have some universally defined probabilistic definitions, when in reality they are entirely subjective. But with coronavirus we need to think in terms of percentages and error bars, and this is deeply unfamiliar territory.

For those prone to worry, the tragic stories of victims in the continuous news cycle can make the virus’s average fatality rate (currently estimated to lie somewhere between 0.5% — 3%) feel many times higher. This is largely due to a phenomenon known as the availability heuristic, a bias that makes us vastly overestimate the likelihood of easy-to-remember events.

For others, a 1% or 2% risk doesn’t sound too bad. In poker terms, 2% is the same chance as your opponent hitting the one exact card they need, like the ace of spades, in order to beat you — slim enough odds to safely ignore. And I would agree with this sentiment if it was purely money on the line.

But when it comes to life-or-death, a 2% risk is extraordinarily high compared to other activities we consider dangerous. For perspective, this is the same mortality risk as two full lifetimes of driving. Even base-jumping — a form of skydiving considered to be one of the most dangerous sports on Earth with its death rate of one in 2,300 per jump — is roughly fifty times safer than contracting coronavirus. It’s also a lot more fun.

While mindless shelf-clearing and extreme quarantining carry their own compounding dangers, I would argue that the consequences of mass-underreaction are worse at this crucial juncture. Thanks to its exponential nature, our window to control the spread of coronavirus is rapidly disappearing, if it hasn’t closed already. But even then, our collective cooperation — such as social distancing — helps distribute the cases over a wider time frame, reducing the pressure on already stretched medical infrastructure.

Poker taught me how infallible our instincts can be in novel, complex, or emotionally charged situations. Pandemics tick all of those boxes. As a result, it is essential we listen to the advice of medical experts over our own gut feelings.

It is a fundamental law of chance that, given enough time, freak events will happen. Yet clearly, we under-valued the risk of a pandemic as a society. Despite a booming economy and a wealth of information at their disposal, governments and individuals were both woefully underprepared.

So as soon as the coronavirus dust settles, we must capitalise on this momentum to plan ahead. Its memory will evaporate fast, and our motivations along with it. The next pandemic — and there will be one — may be even more deadly. But if we start planning now, the coronavirus may turn out to be our best immunisation against it.


Further Listening: This excellent interview with a leading pandemic modeller on 12 ways to stop the next pandemic: