The lives of the self-made often follow a symmetrical curve, wherein a mounting acquisitiveness peaks in middle age and mellows into philanthropy as the person grows in wisdom, leisure time, and (perhaps) abhorrence at the thought of his or her heirs driving around in fancy cars. True to form, Andrew Carnegie devoted his youth to building an empire. By his mid-fifties, when he consolidated his holdings into Carnegie Steel, he was thinking seriously about “the improvement of mankind” and declaring that a “man who dies rich dies disgraced.” After his retirement in 1901, at age 65, Carnegie went on a giving spree that lasted 18 years and dispatched $350 million. Electronics pioneer David Packard traced a similar curve, setting up a modest foundation in his early fifties and, later, in 1988, when he was 75, enriching it with his $2 billion stake in the Hewlett-Packard Co. There is beauty and logic in this progression: first you inhale, then you exhale. But there is also danger in taking it for granted.

Bill Gates, the president of Microsoft, has adopted this curve as a template for his own financial career, perhaps not realizing what a slippery slope he is on. At 41, he has amassed the largest private fortune in the world-currently $23.9 billion, and probably somewhat larger by the time you finish this paragraph. So far, he has barely stopped to exhale. Gates’s charitable expenditures, according to Time, consisted of the following as of January: $34 million to the University of Washington, $15 million to Harvard University, $6 million to Stanford, $3 million in book royalties to inner-city libraries, and $200 million in the form of a foundation fund. By ordinary standards, $258 million is a generous sum. But seen as a mere 1 percent of his net worth, Gates’s philanthropic record is on a par with the average person’s lifetime contribution to wishing-wells.

Gates knows this. It’s all part of a plan he articulates whenever he’s pressed to rationalize his enormous wealth. “Remember,” he told a Playboy interviewer three years ago, “95 percent of it I’m just going to give away… . I’m saving that for when I’m in my fifties. It’s a lot to give away and it’s going to take time.” Until then, Gates is marshalling his excuses. As he frequently reminds people, his billions are tied up in Microsoft stock. So, presumably, if he wanted to liquidate assets, there’d be phone calls to make, papers to sign. A 1991 New York Times profile quoted him as complaining, “I don’t have time to figure out what charities make sense,” to which he added a postscript that set a new standard for procrastination: “And to the degree Microsoft can do well, it’s just that much more to give later.”

It is understandable that somebody in the midst of one of the biggest inhalations in the history of capital might regard the future as his to control. The time and resources at his command appear to be infinite, inexhaustible. He will “give later,” when he reaches a suitable point on the curve. If only the curve of empire building were so predictable.

At Gates’s age, Howard Hughes was a bright young man, too-breaking speed records with his flying and hard at work designing the largest airplane ever built. In his late forties, right on schedule, he turned to philanthropy, using the profits from the Hughes Aircraft Co. to found the Howard Hughes Medical Institute. It seems unlikely that Hughes could have foreseen the years of seclusion and madness that would close out his life. In his waning days he spoke of his interest in supporting medical research, according to James Phelan’s Howard Hughes: The Hidden Years. “Eventually that is where the bulk of my estate will go,” Hughes claimed in an interview. But “eventually” never came: he died intestate, and most of his wealth was divided among his cousins.

The decline of Howard Hughes may be an extreme case, but it is only one of many cautionary tales from which a self-made billionaire might profit. Two of the richest nineteenth-century Americans, John Jacob Astor and Cornelius Vanderbilt, never really got around to major philanthropic works, despite physical and financial longevity. Donald Trump-formerly the Donald, now just a Donald-found that his chance to make a contribution in proportion to his fortune was cut short by the vicissitudes of the market. The list could go on and on. The point is that anyone who counts on a policy of deferred giving is ignoring the role played by Fortune with a capital “F”-kismet, Lady Luck, destiny.

In an uncertain world, the best insurance policy may be to give it while you’ve got it. A living testament to this philosophy is Charles Feeney, cofounder of Duty Free Shoppers, Ltd. In 1984, still in his early fifties, he relinquished the chance to become a Billionaire for Life when he signed over most of his wealth-some $500 million-to the charitable fund he founded, Atlantic Foundation and Atlantic Trust. The fund has since mushroomed to $3.5 billion, according to Newsweek. Another adherent, Percy Ross, a Minneapolis millionaire, looks for unusual ways to brighten people’s lives. He once threw a Christmas Eve dinner for 1,050 disadvantaged children and gave them each a bicycle, for example, and he writes a newspaper column in which he grants readers’ requests for money. “I don’t need any hospital wings or libraries named after me,” Ross told People magazine. “I want to enjoy giving my money away while I’m alive.”

It’s hard to picture Bill Gates handing out bicycles (which, by the way, he could do for every American man, woman, and child). Then again, it’s difficult to imagine how anyone might spend $24 billion. Gates appears confident that the answer will come to him in due season. As his friend and fellow billionaire Warren Buffett has put it, “He will spend time, at some point, thinking about the impact his philanthropy can have. He is too imaginative to just do conventional gifts.” Let us hope that Gates makes up his mind in this lifetime. For when a road is paved only with good intentions, who knows where it might lead?