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.