Panic buying is back in Japan. As the U.S.-Israeli-Iran conflict rattles oil markets, Japanese consumers are stockpiling toilet paper—a product with no connection to the disruptions whatsoever, but that has caused enough problems for the country that the Japanese government has urged citizens to stop buying ahead of time. Still, social media posts depicting empty toilet paper abound. But why would people panic buy goods unrelated to or not affected by the conflict? Panic buying behaves much like a bank run. Nobody knows exactly where it starts—some single, bleating data point that says this store is going to run out...