(This article originally appeared August 5, 2010, on The Chronicle of Philanthropy website.)

In 1889 the steel magnate Andrew Carnegie wrote an essay outlining his "gospel of wealth" to encourage his rich contemporaries to give their money away in the service of society. To his disappointment, none responded.

On Wednesday, Warren Buffett and Bill and Melinda Gates announced that 40 wealthy individuals and families had taken the Giving Pledge in the hope of creating a better world. Are these history's best arm twisters, or is something deeper going on?

In Carnegie's time, big philanthropy barely existed—America's gilded age produced many mansions but few engaged philanthropists.

Today, and in sharp contrast with other countries, many of America's wealthiest (along with others far less well off) routinely make the astonishing personal decision to give away large shares of their hard-earned money (in the aggregate, the equivalent of about 2.2 percent of America's gross domestic product every year). They give to assist the poor, to clean the air, and to champion the rights and freedoms of people around the world.

Who are these people and what do these individuals tell us about how Americans' richest people now view philanthropy?

One of the men who signed the pledge is Julian H. Robertson Jr., founder of the Tiger Management hedge funds. Robertson established Tiger Foundation 20 years ago with two purposes: to break the cycle of poverty in New York City and to cultivate the next generation of active, engaged philanthropists. Tiger Foundation trustees were "tiger cubs"—investment professionals who had made fortunes under Mr. Robertson's tutelage. His rationale?

"It is critical to assign the responsibility of wealth when the wealth is being earned. A decade later, one is already too attached to the money."

In a 2006 act foreshadowing the Giving Pledge, Mr. Robertson increased his personal ante, donating additional millions to the foundation and promising to match further the cubs' donations three to one. The cubs roared back, pledging tens of millions of dollars for a grand total that exceeded $200-million.

Equally important to Mr. Robertson is spending the money wisely. Tiger Foundation invests in dozens of outstanding nonprofit groups including Center for Employment Opportunities, which provides job readiness and placement services for former prisoners; Civic Builders, a nonprofit group that helps high-quality charter schools build modern, low-cost facilities; and Year Up, which serves urban young adults with training programs that offer hands-on skills development, college readiness, and corporate internship opportunities. The foundation invests in these groups the same way its donors invest in companies: with a clear strategy, rigorous due diligence, tight monitoring, and rewards for high performance.

Mr. Robertson appreciates philanthropy's first reality: To make a difference, money must be spent. Had he 'pledged' money to be delivered at some undefined date, nothing would have happened beyond, perhaps, some applause. It takes money in circulation to solve social problems, not money in the bank. The Giving Pledge is thus a potent prelude. To succeed, those dollars must be put to work.

And that raises philanthropy's second reality: Wicked hard problems require wicked smart solutions, backed by relentless persistence. The best solutions emerge through trial and error. It is incredibly hard to give away money in a manner that creates tangible social benefits. Warren Buffett acknowledged this when he "outsourced" his billions of dollars to the Bill and Melinda Gates Foundation.

Mr. Robertson's work demonstrates yet a related third reality: In philanthropy, nothing significant is accomplished by acting alone. Wealth may be earned by individuals, but philanthropists must avoid flying solo. Effective philanthropists collaborate with other philanthropists, with the nonprofit groups they support, and, at their best, with the beneficiaries they are aiming to serve. They understand it’s not about them, it's about delivering results.

Yesterday's announcement shows that a remarkable number of major American donors think this lesson is important enough to be a public cause.

Joel L. Fleishman is a professor of law and public-policy studies and director of the Samuel and Ronnie Heyman Center on Ethics, Public Policy and the Professions at Duke University. Thomas J. Tierney is co-founder and chairman of the Bridgespan Group and a former managing director worldwide of Bain & Company.