ECONOMIC inequality in the United States is at its highest level since the 1930s, yet most Americans remain relatively unconcerned with the issue. Why?

One theory is that Americans accept such inequality because they overestimate the reality of the “American dream” — the idea that any American, with enough resolve and determination, can climb the economic ladder, regardless of where he starts in life. The American dream implies that the greatest economic rewards rightly go to society’s most hard-working and deserving members.

Recently, studies by two independent research teams (each led by an author of this article) found that Americans across the economic spectrum did indeed severely misjudge the amount of upward mobility in society. The data also confirmed the psychological utility of this mistake: Overestimating upward mobility was self-serving for rich and poor people alike. For those who saw themselves as rich and successful, it helped justify their wealth. For the poor, it provided hope for a brighter economic future.

In studies by one author of this article, Shai Davidai, and the Cornell psychologist Thomas Gilovich, published earlier this year in Perspectives on Psychological Science, more than 3,000 respondents viewed a graph of the five income quintiles in American society and were asked to estimate the likelihood that a randomly selected person born to the bottom quintile would move to each of the other income quintiles in his lifetime. These estimates were compared with actual mobility trends documented by the Pew Research Center. Participants in the survey overshot the likelihood of rising from the poorest quintile to one of the three top quintiles by nearly 15 percentage points. (On average, only 30 percent of individuals make that kind of leap.)