What to Do If Your Friends Keep Leaving You Out

Early in Kip Williams’ career as a social psychologist, he was at the park with his dog in Des Moines, Iowa, when a flying disc landed on his blanket. The guys it belonged to were clearly waiting for it, so Williams stood up and tossed it to them. To his surprise, as he prepared to sit down, they threw it back to him. “Suddenly I was part of a three-person toss,” he says. “We didn’t speak to each other or anything; we were just throwing it around. A couple minutes went by, and then, for reasons I still don’t know to this day...