When college students go to dinner, they want the company of their friends in the dining hall and they also want the freedom to go to their phones. To have both at the same time, they observe what some call the “rule of three”: When you are with a group at dinner you have to check that at least three people have their heads up from their phones before you give yourself permission to look down at your phone. So conversation proceeds—but with different people having their “heads up” at different times.
