Because people rarely spend their entire careers at one company anymore, employers have less incentive to invest in training workers in new skills, because they might quit and take those skills to a competitor, said David Deming, a professor of public policy, education and economics at Harvard. Workers also have little incentive to invest in training, because there’s no guarantee it will pay off with long-term employment. Others have trouble thinking of themselves as doing other kinds of jobs — which Lawrence Katz, a Harvard labor economist, says is an identity mismatch, not a skill mismatch.

Even if workers want to learn new skills and find new occupations, there is no streamlined way to do so. People procrastinate, inaccurately assess their own abilities and are unaware of what other jobs entail, according to behavioral economists. The United States spends a fraction of what other developed countries do on labor market adjustment programs like job counseling and retraining. Assistance is piecemeal, and many people who qualify don’t use it.

Meanwhile, employers hire based on credentials that job applicants can’t change — a college degree or previous job title — rather than assessing the skills an applicant has developed, said Mr. Auguste, who was an economic adviser in the Obama administration. He said the approach should instead be, “If you learned it at Harvard or Cal State Northridge or on the job as a secretary or in the Navy or as a volunteer, awesome.”

Laurel Yoder’s career is an example of how jobs can overlap in unexpected ways. She was a paralegal for six years, until she attended a friend’s childbirth and decided to become a doula, helping women in labor. She eventually went back to school to get degrees in nursing and midwifery, and is now a nurse-midwife in St. Joseph, Mich.

The two jobs have more skills in common than it might seem, she said, like “knowing how to be concise and thorough and document clearly so your colleague can follow your thought process.”