Lurking behind the question of jobs — whether there are enough of them, how hard we should work at them, and what kind the future will bring — is a major problem of job engagement. Too many people are tuned out, turned off, or ready to leave. But there’s one striking exception.

The happiest people I know are dedicated to dealing with the most difficult problems. Turning around inner city schools. Finding solutions to homelessness or unsafe drinking water. Supporting children with terminal illnesses. They face the seemingly worst of the world with a conviction that they can do something about it and serve others.

Ellen Goodman, a Pulitzer Prize-winning journalist (and long-time friend), has turned grief to social purpose. She was distraught over the treatment of her dying mother. After leaving her job as a syndicated columnist, she founded The Conversation Project, a campaign to get every family to face the difficult task of talking about death and end-of-life care.

Gilberto Dimenstein, another writer-turned-activist in Brazil, spreads happiness through social entrepreneurship. When famous Brazilian pianist Joao Carlos Martins lost the use of most of his fingers and almost gave into deepest despair, Dimenstein urged him to teach music to disadvantaged young people. A few years later, Martins, now a conductor, exudes happiness. He has nurtured musical talent throughout Brazil, brought his youth orchestras to play at Carnegie Hall and Lincoln Center in New York, and has even regained some use of his fingers.

For many social entrepreneurs, happiness comes from the feeling they are making a difference.

I see that same spirit in business teams creating new initiatives that they believe in. Gillette’s Himalayan project team took on the challenge of changing the way men shave in India, where the common practice of barbers using rusty blades broken in two caused bloody infections. A team member who initially didn’t want to leave Boston for India found it his most inspiring assignment. Similarly, Procter & Gamble’s Pampers team in Nigeria find happiness facing the problem of infant mortality and devising solutions, such as mobile clinics that sent a physician and two nurses to areas lacking access to health care.

In research for my book Evolve!, I identified three primary sources of motivation in high-innovation companies: mastery, membership, and meaning. Another M, money, turned out to be a distant fourth. Money acted as a scorecard, but it did not get people up-and-at ’em for the daily work, nor did it help people go home every day with a feeling of fulfillment.

People can be inspired to meet stretch goals and tackle impossible challenges if they care about the outcome. I’ll never forget the story of how a new general manager of the Daimler Benz operations in South Africa raised productivity and quality at the end of the apartheid era by giving the workers something to do that they valued: make a car for Nelson Mandela, just released from prison. A plant plagued by lost days, sluggish workers, and high rates of defects produced the car in record time with close to zero defects. The pride in giving Mandela the Mercedes, plus the feeling of achievement, helped the workers maintain a new level of performance. People stuck in boring, rote jobs will spring into action for causes they care about.

Heart-wrenching emotion also helps cultivate a human connection. It is hard to feel alone, or to whine about small things, when faced with really big matters of deprivation, poverty, and life or death. Social bonds and a feeling of membership augment the meaning that comes from values-based work.

Of course, daunting challenges can be demoralizing at times. City Year corps members working with at-risk middle school students with failing grades from dysfunctional homes see improvement one day, only to have new problems arise the next. Progress isn’t linear; it might not be apparent until after many long days of hard work have accumulated. It may show up in small victories, like a D student suddenly raising his hand in class because he understands the math principle. (I see this from service on the City Year board. You can find dozens of these stories on Twitter under #makebetterhappen.)

It’s now common to say that purpose is at the heart of leadership, and people should find their purpose and passion. I’d like to go a step further and urge that everyone regardless of their work situation, have a sense of responsibility for at least one aspect of changing the world. It’s as though we all have two jobs: our immediate tasks and the chance to make a difference.

Leaders everywhere should remember the M’s of motivation: mastery, membership, and meaning. Tapping these non-monetary rewards (while paying fairly) are central to engagement and happiness. And they are also likely to produce innovative solutions to difficult problems.