Helicopters got to Wilmington, North Carolina, after a day of isolation; Hurricane Florence made landfall there, and the city, with one foot in the Atlantic and the other in the Cape Fear River, soon became an island. Its main roads underwater, Wilmington went without help until boats and choppers reached it with medical supplies, water, and food.

But it only took a day. According to the federal government, that’s actually pretty fast. Since the terrorist attacks of September 11, 2001—or at least since Hurricane Katrina hit New Orleans in 2005—the government has urged all of us, every individual, to be ready to go without help for at least three days in the wake of a disaster. You’re supposed to have kits in your cars and at home … maybe not the shopping cart from The Road, but just, like, be ready, OK? And now with Florence a waning threat but with fires and storms an apparently permanent part of Earth’s changed climate (and earthquakes, volcanoes, and terror always possible), the rules seem to be shifting a bit again. The new message: Be ready for 14 days on your own. Two weeks.

That’s a lot of supplies to buy and store—especially when the whole idea of home disaster preparedness kits is based much more in conventional wisdom than actual data. On the other hand, one might save your life. Good luck, everyone!

Recommendations for what’s supposed to go in these kits vary, but basically it’s a gallon of water per person per day and food, too, plus medicines, blankets and sleeping bags, maybe a tent, extra eyeglasses, lots of batteries, something to make light with, something to make fire with, maybe a hand-cranked radio.

All that makes sense. “It is not realistic, even in developed countries, to expect that the governmental infrastructure will be able to reach everyone within hours,” says Daniel Barnett, a disaster preparedness researcher at the Johns Hopkins Bloomberg School of Public Health. “Individuals need to have self-sustainability.” At minimum, you want to take as much pressure off of first responders as possible so they can triage effectively, attending to life-threatening situations while you chill in your backyard, if you’re able. That’s part of supporting what disaster pros call “resiliency,” the ability of a community or region to withstand whatever it gets punched with. It’s supposed to be interpersonal, too—neighbor to neighbor.

The problem with all that is, as Barnett and his colleagues showed in a 2012 review of the literature, almost no one actually builds kits. Well, perhaps fewer than half overall, but results varied wildly by region—as low as 7.4 percent in northeastern Alabama, much higher in post-Katrina New Orleans (85 percent of survey respondents had a disaster plan, but only 22 percent had a kit). Partially that’s out of inertia, laziness, fear—all the things that keep everyone from preparing for anything. But also, older, better-educated, wealthier, home-ownier people were more likely to have kits than younger, less-educated, poorer people. And of course, poorer people are the ones who get hurt the most by disasters in the first place.

A couple of years ago things got even more complicated. In 2016 the Washington Military Department, essentially that state’s National Guard, ran an exercise called Cascadia Rising. The idea was to simulate a response to an earthquake and subsequent tsunami emanating from the Cascadia Subduction Zone off the Pacific Northwest, subject of a much-read New Yorker article from the previous year. “Cascadia Rising was a massive eye-opener,” says Karina Shagren, spokesperson for the Washington Military Department. “We realized there would be pockets of communities that won’t receive help for several days, if not several weeks.” Washington’s coastal communities would lose the bridges that connect them to the rest of the world. They’d have to wait for help by air or sea.