“In the past, getting to early retirement was a badge of success,” said Marc Freedman, founder of Encore.org, an organization that helps people find opportunities in the second half of life. “Now many find themselves in an identity free fall as their first acts conclude. They realize their sense of self was tied up in the important work they were doing. They become what we jokingly call a P.I.P., a ‘previously important person.’ ”

Consider the challenge for these people of attending a cocktail party and being asked what they do. Do they say what they did, or what they do now? These concerns have led some former business owners to redeploy their skills and resources in a second act — but not necessarily in the same way they did the first time around.

While an entrepreneur’s first act is generally about building something impressive and making money, said Jennifer Kalita, a consultant and business coach in the Washington area, the second act is typically more personal and less focused on money. “The entrepreneur has already proven something to himself and others,” she said. “He and we know he can do it. The second act is more about what he wants to do — for his customers, for the environment, and for the legacy he wishes to leave.”

For example, Jay Coen Gilbert, 47, a founder of the footwear and apparel line AND1, sold his company and founded B Lab, the driver behind the B Corp movement that promotes businesses that try to have a positive impact on society or on the environment. And Chris Crane, 63, led his commercial real estate database company, Comps InfoSystems, through a successful initial public offering and then went on to found Edify, a nonprofit organization in San Diego that lends money to profit-seeking private schools in countries like Rwanda and Liberia.

After the sale of KCC, Mr. Carson had a chance conversation with a family friend who helped him realize that he wanted to build another company, but one with a social mission. The opportunity came from another friend who had tinkered with a technology that could produce potable water from moisture in the air.