Why do experts say quarantines and canceled events are a good idea for controlling the spread of the coronavirus, especially when they involve people who are not sick?

It's all in the numbers and how quickly they grow.

Health officials are trying to avoid a rapid spike of cases that could overwhelm the health care system by "flattening the curve," or spreading out the number of coronavirus cases over a longer period.

In many respects, it's not whether the situation is going to get worse but how quickly.

“Whenever you have an outbreak that you can start seeing community spread ... when you have enough of that, then it becomes a situation where you’re not going to be able to effectively and efficiently contain it,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told a House committee Wednesday.

"Bottom line, it's going to get worse," he said.

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How much worse, he said, depends on the ability to contain those infected.

That's where the curve comes in – a visual measure of the two ways efforts to contain the virus could unfold.

If it happens too quickly, there will not be enough hospital beds or ventilators for treating all patients. More people will die.

In a graph, the difference is visually stunning.

In the worst-case scenario, the daily number of cases jump dramatically, rapidly forming a tall peak that breaks through the critical line marking the capacity of the health care system. The reality is stark: Too many cases too soon and they overwhelm the hospitals.

By spreading the cases over a longer period, the numbers grow, but more slowly, forming not a mountain but a stubbier, longer sand dune. The cases grow and peak, but stay below the health care system capacity line. The system can absorb them.

By "flattening the curve," epidemiologists hope to turn a mountain into a mole hill.

“Even if we can’t change the total number of people who are going to be infected, by keeping the total numbers low at any given time, that dramatically improves our ability to cope with the outbreak and in particular to provide care for the people who are going to be severely ill," Emily Gurley, an associate scientist in the Department of Epidemiology at the Johns Hopkins Bloomberg School of Public Health, told USA TODAY.

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The original graphic, created by the Centers for Disease Control and Prevention, has quickly become popular with the help of the #FlattenTheCurve hashtag on Twitter.

In flattening the curve, the goal is not so much to reduce the total number of people getting sick but to slow the rate at which they do.

The ability for the health care system to care for patients "is much better if they come in small doses," said Gurley, an expert in infectious diseases.

“Our best guess is that most people are going to get this virus at some point. There’s not much we can do about that without effective vaccines," Gurley said. "But our ability to appropriately treat patients and for society to accommodate and care for these patients and cope is much better if infections don’t occur all at the same time.

"The public health goal is to keep the number of new cases happening at any given time as low as possible, as long as possible,” she said.

Keeping people apart – by canceling big public gatherings, encouraging people to stay at home and urging those who go out to maintain distance from others – reduces the opportunity, and pace, of the spread of the disease.

Simple, really. If few people get out in the rain, fewer will get wet.

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