[T]oday’s typical man is seen as independent, ambitious and competitive, naturally suited to market work and the breadwinner role. Meanwhile, today’s typical woman is seen as nurturing, expressive and responsive to the needs of others, naturally suited to homemaking and the emotional work required by secretaries, flight attendants and nurses. These basic tenets of separate spheres continue to shape our default understandings of men and women, reproducing stereotypes that systematically advantage men and disadvantage women in the workplace.

These stereotypes lead to powerful social expectations that link our sense of what one needs to be successful in historically male professions to masculine personality traits and traditionally masculine life patterns. One prominent physicist put it this way: “In particular, our selection procedures tend to select not only for talents that are directly relevant to success in science, but also for assertiveness and single-mindedness.” In other words, physicists are expected to have stereotypically masculine personality traits: to be forceful, proactive, assertive—”agentic,” to use social psychologists’ chosen term.

Physicists, the quote reminds us, are expected to be not only assertive but also single-minded. Hard-driving lawyers, neurosurgeons and investment bankers—indeed, all historically male high-status jobs—also require some version of assertiveness and single-mindedness. In other words, such jobs are designed around masculinity and men.

Masculinity holds the key to understanding why the gender revolution has stalled.