When it gave permission to fully vaccinated Americans to shed their masks in many situations, the Centers for Disease Control and Prevention made a tacit gamble: that easing mask rules will inspire more people to get vaccinated against COVID-19. But that’s far from a sure bet, say experts who study human behavior. “It’s a big ol’ experiment,” says Katherine Milkman of the University of Pennsylvania’s Wharton School, an economics professor who studies what inspires behavioral change. Milkman is fully vaccinated but — like many people — has grown accustomed to wearing a mask. Read and listen more at NPR.