Have you ever been angry when someone cut in line? In 1986, researchers in New York reported an experiment. A person stepped into real lines, for example at ticket windows. Who complained?

Most of the complaints came from people behind the person who cut in. The people in front did not care much. Waiting one more minute is a small loss, but people also feel it is unfair.

Stanley Milgram is famous for his obedience experiment, but he also studied what happens when someone cuts in line. In a 1986 study, researchers stepped into about 130 real lines in New York, such as lines at ticket counters. They went in between the third and fourth people.

In a large share of lines, someone objected. Objections were even more common when two people cut in. Most complaints came from people standing behind the intruder. People in front, who did not have to wait longer, rarely reacted.

When a silent helper stood right behind the intruder, protests dropped sharply. The researchers argued that a line is a small social system with shared rules. People get angry over a short wait because cutting in breaks their sense of fairness.

Why does a stranger stepping into a queue irritate us so much when it costs us only a minute or two? In 1986, Stanley Milgram and his colleagues reported a bold field experiment in New York on the question. At around 130 waiting lines, an experimenter politely announced that they wanted to get in and inserted themselves between the third and fourth people.

The researchers varied the number of intruders and whether silent confederates acted as "buffers" behind them. A single intrusion drew objections in a considerable proportion of lines, and two intruders drew even more. Most of the objections came from people behind the point of intrusion. Those in front, whose waiting time was unaffected, rarely responded.

When buffers stood silently behind the intruder, protests fell markedly, apparently because the people further back felt that the duty to object belonged to the person directly behind. Self-interest alone cannot explain why people accept the awkwardness of confronting a stranger over so small a loss. The researchers saw the queue as a social system governed by an unspoken first-come, first-served rule. Later work on fairness, including research on how people reject unfair offers in money-sharing games, supports that view.