Every major public event that happens—every NHL game, every pre-season game, every parade, every conference, every protest, every Mass—has a likelihood of spreading the virus not only to attendees, but then to those who subsequently come into contact with the attendees.

If would-be attendees stay closer to home, they prevent (or at least delay) the spread of the virus from the places where it’s already present to cities and towns where it’s absent. If you keep your kids home from school, they are less likely to get it, and less likely to give it to someone else. If you cancel your pick-up basketball games, you decrease the odds that your neighbor with coronavirus will give it to others.

According to models, a 25% reduction in contacts yields a 50% reduction in infections.

So schools are going to close. Daycare is going to close. Flights will be canceled. You won’t be allowed to visit your mom or grandma at the nursing home. Your Friday Fish Fry isn’t going to happen. We may not shut down as totally as Italy has, but we’ll soon be closer to where Italy is today than to where the U.S. was on Monday.