Lessons from a toilet paper shortage

Have you ever thought about how weird the question “Can you pass the salt?” is?

It’s an innocuous question that most of us have asked over the dinner table at some point. It’s also a deeply loaded one. When you ask me if I can pass the salt, you are not actually wondering whether I am physically capable of lifting a salt shaker—you want me to hand it to you. But since it feels rude to command someone to pass the salt, the request is couched as a related but different question. And here’s the weirdest part: It works.

Why? Because of something called common knowledge. I know you really mean “Pass me the salt.” And you know I know that. And because both of us know what each other knows, an indirect question is, in reality, super clear.

If that makes your head spin, I get it. Common knowledge is strangely complicated for something so commonplace. Luckily, Steven Pinker explains the topic brilliantly in his latest book, When Everyone Knows That Everyone Knows.

Steven is a cognitive psychologist, and I’m a big fan of his books, which always illuminate something new and fascinating about how humans interact. In this one, he writes about how common knowledge is key to the fabric of social behavior. As Steven explains, it allows “individual minds [to] coordinate their choices for mutual benefit. Many of our harmonies and discords fall out of our struggles to achieve, sustain, or prevent common knowledge.”

The book starts with the famous story of The Emperor’s New Clothes. As soon as a child points out the obvious—the fact that emperor isn’t wearing any clothes—the entire town realizes everyone knows that the emperor is naked and turns on him.

It sounds like a silly folktale until you realize that it reveals a fundamental truth: The social dynamic changes as soon as I know that you know what I know. In this case, people feel more comfortable speaking out publicly once they realize others see the same thing. Common knowledge makes coordination easier, whether it’s something as small as passing the salt or something as big as a protest against an unfair policy.

Common knowledge is a powerful communications tool, but it can also cause chaos. In the book, Steven explains a phenomenon that has baffled me for years: panic-buying toilet paper during an emergency. As far as I know, toilet paper manufacturers have never struggled to meet demand. And yet, every time there’s an emergency—whether it’s a hurricane, a snowstorm, or a pandemic—people rush to the store and clear toilet paper off the shelves.

Steven traces the blame back to Johnny Carson. In 1973, the U.S. was reeling from shortages of gasoline and staples like sugar. Johnny made a joke in his monologue on The Tonight Show about the country running low on toilet paper. “It wasn’t true at the time,” writes Steven, “but it quickly became true when viewers, knowing how many other Americans were viewers, snapped up the supply.” Ever since, the common knowledge that toilet paper is scarce during emergencies causes people to buy it in bulk, which makes toilet paper scarce during emergencies.

The book is full of recursive examples like this that make your head hurt while revealing deep insights about how we communicate. There aren’t many other mainstream books about this topic, and it provides a kind of groundbreaking way of thinking about human behavior. (Steven sent me an early copy of the book, and I enjoyed it so much that I provided a blurb for the cover.)

The chapter that interested me most is about one of my favorite topics: philanthropy. Steven and his colleagues ran numerous experiments to learn how people feel about different kinds of philanthropy. They found that people see anonymous giving as significantly more virtuous than public giving. As soon as a donation becomes common knowledge, it becomes less impressive. This belief is so strong that some participants in Steven’s research believed a smaller amount given anonymously was better than a larger amount given publicly.

I think there are a lot of practical reasons to be open about your giving, including the fact it creates transparency. But it was helpful to understand more about how people see philanthropy—and how those beliefs might shape their motivations for donating. I spend a lot of time encouraging other wealthy people to give away their money. This book armed me with new information that will (hopefully) make those conversations more effective moving forward.

Most people would benefit from understanding how common knowledge props up every conversation we have. “Human social life can seem baffling,” Steven writes. “It is played out with rituals and symbols and ceremonies, rife with social paradoxes and strategic absurdities… [but] life provides people with opportunities to flourish if they coordinate their actions.” If you are interested in learning more about how humans communicate and work together, I highly recommend reading When Everyone Knows That Everyone Knows.