The firm, Dimensional Fund Advisors, was co-founded by David Booth, who had worked at the University of Chicago as an assistant to Eugene Fama. As a graduate student in the early 1960s, Fama coined the phrase efficient markets. D.F.A. sold its clients on passive investing: Instead of looking for trading opportunities and paying stockbrokers and fund managers, D.F.A. bought and held baskets of stocks chosen for the sort of risk they represented. It didn’t call these baskets index funds, but that is more or less what they were. And they—along with the idea they embodied—were growing at a sensational rate. In 1989, D.F.A. was managing $5.2 billion; by 1998, the number was up to $28 billion. Then the internet bubble burst, and even more people fled the stock-picking game. In the summer of 2007, when I visited, the firm had an astonishing $153 billion under management, $90 billion of which had come from individual investors, through a network of professional advisers.

Back in the old days, when investors believed that they were paying for some mysterious wisdom, the buildings housing Wall Street firms were stone on the outside and dark wood on the inside. Now that investors have learned to fear what they can’t see, the firms are in buildings made of as much glass as can be incorporated into a structure without compromising its ability to stand. The day I arrive at D.F.A.'s offices, I find 150 financial advisers in a glass box, waiting to be educated in a seminar that lays out the D.F.A. way. The coffee and pastries are free, the men and women wear suits, and the conference room has the antiseptic feel of any other 21st-century firm. But the atmosphere is entirely different from Wall Street. There’s no chitchat about the market, even though it has been bouncing around wildly. Instead, two speakers discuss how, knowing what we now know, anyone could present himself as a stock-picking guru. "If you put a thousand people in barrels and push them over Niagara Falls," one of them says, "some of them will survive. And if you take those guys and push them over again, some of them will survive. And they’ll write books about how to survive being pushed over Niagara Falls in a barrel."

The other speaker paces back and forth in the well at the front of the room. "Have you seen the show Mad Money?" he says. "It's repulsive."

No one disagrees. That they are here, preparing to join the thousand or so converts authorized to sell D.F.A.'s funds to investors, implies their agreement. They're all salesmen, but salesmen peddling an odd idea: Don't listen to salesmen.

In the beginning, back in the 1980s, D.F.A. didn’t sell to individual investors at all. The funds sold themselves by word of mouth. Finally in 1989, D.F.A., with some reluctance, agreed to allow financial advisers to steer clients’ money into D.F.A. funds, but only after those advisers had demonstrated their purity of heart. They must never, ever, sell individual stocks, try to time the market, or suggest to investors that it is possible to systematically beat the market. D.F.A. required its aspiring antisalespeople to fill out questionnaires and submit to telephone interviews. If they passed those tests—which thousands failed—a team from the firm would dignify them with an office visit and grill them on their beliefs about the stock market. "One of the reasons we visit them,” says Weston Wellington, one of D.F.A.'s principals, "is just to see the office. If there are TVs blaring CNBC and people running around screaming, we say, 'Wait a minute here.' " The final test of ideology is the conference. Having demonstrated sufficient cynicism about Wall Street, the financial advisers must pay their own way to Santa Monica, California, and listen to speeches that explain why, if anything, they should think even less of Wall Street than they already do.

One question naturally arises: What makes someone good at selling this curious attack on the modern financial system? I ask Joe Chrisman, the interface between D.F.A. and the thousand independent financial advisers who have qualified to sell D.F.A. funds, "Of all these proselytizers, who is the most effective at taking an investor who thinks he can beat the market and turning him into someone who quits trading and hands his money over to D.F.A.?"

"That's easy," he says. "Blaine Lourd."

When Blaine Lourd started out on Wall Street, he had a mop of dark hair and the wild smile of a Baroque painter’s idea of Bacchus. He was still young, thin, and handsome, but as his career progressed, the smile changed, becoming, like his eyes, narrower and more calculating. He was turning into one of those men that old friends fail to recognize at their 20-year high-school reunions. But here was the thing: The difference between who Blaine had been and who he had become was entirely a matter of how he had set about making himself a success. He’d been raised to go through life happy, without thinking too much about it, but the career he’d chosen had proved contrary to his upbringing. He’d violated his nature, and his appearance was paying the fine.