In a 2009 study of 450,000 Americans, the economists Angus Deaton and Daniel Kahneman discovered that for Americans happiness seemed to level off at a household income level of $75,000. Earnings beyond that, even far beyond that, didn’t seem to make people much happier. Interestingly, the $75,000 limit had nothing to do with the cost of living; people were just as happy earning $75,000 in expensive cities like New York as they were in much lower-cost cities. One reason for this may be that although the cost of housing is higher in larger cities, the cost of transportation and food is lower, and there is a much larger selection of goods and services. In fact, as the size of a city doubles, the number of things to buy increases by 20 percent, and their cost declines by 4.2 percent.

But there is a deeper reason. Happiness is tied to what Deaton calls emotionally enriching social experiences. Kahneman says, “The very best thing that can happen to people is to spend time with other people they like. That is when they are happiest.” The way people spend their time is also a critical component of sense of well-being. In another study Kahneman and his colleagues tracked how people experience their day by asking them to record events in fifteen-minute intervals and evaluate them. Walking, making love, exercise, playing, and reading ranked as their most pleasurable activities. Their least happy activities? Work, commuting, child care, and personal computer time. How many people really enjoy a night of plowing through endless emails?

This survey should not mislead us about the value of work. Work can be deeply gratifying and meaningful, and it can also provide rich social relations. Employment is a key element of well-being. People who are unemployed or underemployed are statistically more likely to die younger and be in worse health. People who lose their job in middle age and have difficulty finding a new one are more likely to become depressed, and have a two to three times higher risk of heart attack and stroke over the next ten years. So one of the key challenges of cities in the 21st century is to develop economies that generate stimulating, productive work for all of their residents.

In the past people often held the same job for life, whether as a shepherd, a member of a medieval guild, or an employee of a large corporation. Today the average Millennial will have had 11 jobs by the time he or she reaches the age of 40. This underscores the need to acquire many different skills beyond technical ability. Satisfying work often requires not only a high level of education, but the emotional and social intelligence required to work successfully in teams. This wider range of qualifications will be essential in a world where computer coding may become the entry-level position that a factory job once was. As agriculture becomes more and more industrialized, rural people are flocking to cities seeking work. Yet with robots increasingly taking line positions in factories, there are likely to be fewer jobs for the uneducated in the future.