Now We Can Actually Count and Track the 'Familiar Strangers' in Our Lives

The social psychologist Stanley Milgram is best known for conducting his infamous shock experiments (or perhaps to some for identifying the "six degrees of separation" that govern human connections), but he also produced a lot of insights about the peculiarities of city life. One thing Milgram noticed was the way that city residents will often encounter the same stranger time and again — the "familiar stranger," he called this person in an essay from 1972:

A few years before Milgram wrote that essay, his students did a rudimentary study to see just how common the "familiar stranger" phenomenon was. They photographed people at a commuter station one morning, returned the following week to hand out the photographs, and asked people to pick out the faces they recognized. About 90 percent of people had at least one "familiar stranger" in their lives, and the average person had about four.