The subjects that people joke about are likely to be things that make them feel unsure or uncomfortable, as with questions about religion, politics, sex, and ethnic differences. People joke about these subjects as a way of releasing feelings of tension and also as a way of sending up trial balloons. If they say something that does not go over well, they can backtrack and hide behind the cliché, "I was only kidding."
At a 1984 humor conference held at Arizona State University, Robert Priest, a psychologist at West Point, reported on his Moderate Intergroup Conflict Humor (MICH) theory. He agreed that for people to be inspired to create a joke they must feel some tension, but he argued that joking will relieve only moderate levels of tension. If groups or individuals are feeling strong—rather than moderate—levels of tension, they will feel frustrated rather than satisfied by jokes. He illustrated his point by showing how history is filled with jokes about the so-called battle of the sexes, but in the late 1970s and the 1980s, as the feminist movement developed and hostilities between men and women increased, sexist joking was no longer viewed as humor. Instead, it was viewed as aggression, and those who told sexist jokes were taken to court and punished for creating hostile workplaces.
A related way of explaining this idea that people need some distance from a problem before they can find humor in it is the statement that "tragedy plus time equals humor." James Thurber has been credited with this observation, but many people, including Steve Allen and Bob Hope, have commented on the idea. After the September 11, 2001, tragedy, it was a topic of general public discussion when comedy clubs and late-night comedians took time off.