The four simulations you just watched — a free-for-all, an attempted quarantine, moderate social distancing and extensive social distancing — were random. That means the results of each one were unique to your reading of this article; if you scroll up and rerun the simulations, or if you revisit this page later, your results will change.

Even with different results, moderate social distancing will usually outperform the attempted quarantine, and extensive social distancing usually works best of all. Below is a comparison of your results.

Simulitis is not covid-19, and these simulations vastly oversimplify the complexity of real life. Yet just as simultis spread through the networks of bouncing balls on your screen, covid-19 is spreading through our human networks — through our countries, our towns, our workplaces, our families. And, like a ball bouncing across the screen, a single person’s behavior can cause ripple effects that touch faraway people.