If there is one cardinal rule of the Forbes 400, it is this: If you don't inherit money, the likeliest route to making a real bundle is by taking a lot of risks.

It's not for nothing that the 400 is bursting with card sharks and poker players. Hedge fund honcho Steve Cohen played all-night poker games during high school. Media magnate John Kluge spent his college days playing poker and graduated from Columbia University in 1937 with $7,000 in winnings. Takeover artist Henry Kravis whiled away the hours waiting on a 1986 deal to acquire conglomerate Beatrice Companies by playing poker.

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"I'd just won a hand and was raking in the pot when the good news came," Kravis said at the time. And odd couple Bill Gates and Warren Buffett, two of the wealthiest men in U.S. history, are fond of playing poker and bridge together.

Many of the Forbes 400 have been willing to take gargantuan risks, sometimes a number of times, in order to realize their dreams. Toy salesman Ty Warner mortgaged his home and invested his life savings to launch Beanie Babies. Paul Fireman put his home in hock for the U.S. distribution rights to a small British shoe company called Reebok.

And even when they make it to the top, many of the 400 do not stop gambling. Donald Trump borrowed hundreds of millions of dollars to build on his father's substantial real-estate empire. And oilman and corporate raider T. Boone Pickens bet his entire company, Mesa Petroleum, which he had spent most of his life building, on his instinct that the falling price of natural gas would eventually go up. With the benefit of hindsight, it's easy to see how these men succeeded. But at the time their gambles appeared to be edge-of-the-seat risks, if not to the headstrong individuals themselves, then at least to outsiders.

In many cases, Forbes 400 types seem to have a different perception of risk than the average person. Risk-takers have to be able to think big, and they have to be able to leverage those big ideas with whatever assets they have at hand: homes, real estate, the shirt off their back. To succeed, they also have to be 100% focused on winning and have the confidence to go against the conventional wisdom. Conversely, and this may be the key point for many who have made it onto the Forbes list, they have to know how to avoid disaster, evaluating the risks well enough to ensure that failure doesn't wipe them out.

The saga of Haroldson Lafayette Hunt illustrates both the upside and the downside of the gambling instinct that permeates the Forbes 400. When his father died in 1911, H.L., then 22, set out to earn his fortune. He wanted to be a cotton farmer, but fate dealt him a different hand: His cotton crop was wiped out in the first flooding to hit the area in 35 years. And so the young man was forced to turn to a vocation he already knew well. He had proved to be an ace card player in his previous travels as a teenager, earning himself the nickname Arizona Slim. Hunt stayed afloat through those difficult years in Arkansas playing cards day and night.

Hunt eventually opened a gambling hall in El Dorado, Ark., invested in his first oil leases, and struck oil with his first well. But it wasn't until he signed a deal in November 1930 to take over the lease of the Daisy Bradford No. 3, a well in the East Texas oil field, that he hit the jackpot. The well was situated in an extremely productive section of the biggest oil find of the early 20th century. And it was the basis for Hunt's future oil empire, which would later be estimated at $2 billion.

In his biography of the Hunt family, Texas Rich: The Hunt Dynasty, from the Early Oil Days Through the Silver Crash, Harry Hurt III noted that Hunt was "a man of contradictions and eccentricities ... but, at heart, he was still a gambler. He craved new opportunities to make money--not because he wanted possessions per se, but because the gambler in him wanted to see if he could run up the score. Specifically, Hunt wanted to put his profits from East Texas into new drilling ventures, for, as he saw it, 'the more wells you drill, the greater chance you have of finding oil.' "

And all the time that Hunt poured money into new wells, he continued to gamble, as well. The wildcatter once placed a $200,000 bet on a football game. Another time he came from $10,000 down to win more than $100,000 from a professional Las Vegas gambler.

Death may have cheated Hunt, who died in 1974, out of his place on the 400 list, which debuted in 1982. But he was the self-proclaimed richest man in America in his day. (His descendants, however, made a strong showing in that first Forbes special issue, with 12 places on the list.) And like Hunt, most members of the Forbes 400 are self-made: 70% in 2006. So it's all the more noteworthy that so many of them are willing not only to take chances with their fortunes, but also seem to take outsize chances.

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Jon Huntsman, whom TV talk-show host Larry King once described as "the most remarkable billionaire most of America has never heard of," is one such master risk-taker. In the late 1970s, Huntsman, a devout Mormon, father of nine and already a multimillionaire, headed to Washington, D.C., to carry out missionary work. When he returned to Salt Lake City in 1982, at the age of 45, he embarked on his riskiest venture yet--the purchase of a $42 million polystyrene plant from Shell Oil.

It was the depths of the recession, and polystyrene, a kind of plastic used in everything from food packaging to cutlery, was in oversupply. Like many big firms, Shell was desperate to get rid of the plant that it had originally bought for $67 million--so desperate that it was willing to sell the plant at a loss. But who would want to go against prevailing wisdom and buy it? It turned out that Huntsman would.

First he borrowed $500,000 against his house and $1.3 million against assets, including a restaurant. Then he approached petroleum firm ARCO. He asked the company to lend him $10 million. In return, he promised to buy 150 million pounds of raw materials from ARCO every year for the next 13 years. Finally, he persuaded Shell to guarantee $12 million of a $29 million bank loan and to defer $3 million of the purchase price until later. With that, Huntsman bought the plant.

Although most of the financing came from other people's pockets, as is frequently the case with the biggest risk-takers, Huntsman says he could not have convinced any of the other parties to buy in if he hadn't been prepared to put all his possessions on the line: "They want to see some type of equity, and if you don't have a rich uncle, the only equity you can put up is whatever you own--your house and any other assets you may have. They may not amount to much, but at least it's everything you've got. Then they can believe you. And that's more important to most people than the equity you put up."

And while Huntsman concedes that he took a risk, he believes that there was nothing reckless in his decision. "I thought I had studied my economics well and studied my supply demand curves, and as it turned out, I was right," says Huntsman. "Within a few years I broke even, and then the gold hit, and I made hundreds of millions of dollars from a very modest investment."

If only it was so easy. A couple of years after he bought the Shell plant, the industry was still in recession and Huntsman was still in financial trouble. Not only did he refuse to give up but, convinced that the market was about to turn upward, he continued his acquisitions and bought three more plants. Eventually, the markets, of course, did improve.

So what is it about risk-takers that allows them to pursue one death-defying deal after the next? It comes down to this: If you're going to take massive risks, you simply can't perceive huge personal debt as the catastrophe that it would be to most people. In fact, the hallmark of risk-taking may well be such an unshakable confidence in success that it overwhelms any concern for failure.

Andrew Keyt, executive director of the Chicago Family Business Center at Loyola University, says that although entrepreneurs experience anxiety about their businesses, their fears are overridden by a sense of purpose and a supreme confidence in their ability.

That certainly seems the case with Sheldon Adelson, who, like Huntsman and the other 400 members, embodies the self-confidence of a riverboat gambler. The son of a Boston taxi driver, Adelson made his debut on the Forbes 400 in 1995 with a net worth of $360 million, thanks to his creation of the giant annual Computer Dealer's Exhibition (COMDEX) in Las Vegas. But he owes his multibillion-dollar fortune to the hotel-casino industry.

Seated in a conference room at a New York public-relations firm, the pugnacious billionaire claims fearlessness is essential. "The reality is a lot of people have good ideas," Adelson says. "I am not the only guy in the world with good ideas. But people are afraid to lose, and one of the main characteristics of practicing entrepreneurship is to be unafraid of losing. If you are afraid of losing you will never attack something. It's good to have a risk-taking mentality. Even if I do lose I am not frightened to get up and try again."

Adelson showed no fear in his attack on the Vegas gaming and hotel industry. In 1995 he sold COMDEX for $862 million (Adelson's stake was worth $510 million). Rather than cash in his chips, he plowed them right back into a new venture. He demolished the loss-making Sands Hotel, which he had bought in 1989, and built in its place the 4,000-room Venetian at a cost of $1.5 billion. Adelson's stake in the venture was almost $450 million in cash and land, with a further $500 million raised in bonds underwritten by Goldman Sachs.

Before Adelson, Vegas hotels ignored the midweek convention-goers, who were seen as low spenders. But the opulent Venetian was designed to attract the business visitor. Every room in the hotel is a minimum 700 square feet in size. Facilities include faxes, minibars and food cooked by top chefs. The Vegas Old Guard said it would never work. But it did.

And Adelson didn't stop there. In 2004 he opened the Sands Macau in China. A former Portuguese colony that was handed back to the Chinese in 1999, Macau is the only place in China where gambling is legal. As such, it is a new battleground for the gaming industry.

Chinese billionaire Stanley Ho monopolized the Macau gaming industry for decades. But in 2002 authorities ended his reign, opening up licenses to outside competitors. While other investors hemmed and hawed over gaming regulations, Adelson threw himself into the fray. He gambled $265 million on the Sands Macau, a casino-only venture that was built in just 14 months.

The Sands Macau raked in $400 million in revenues in its first year. That same year, Adelson took Las Vegas Sands public, and his net worth exploded from $3 billion in the fall of 2004 to $11.5 billion in the spring of 2005. By 2007, his fortune had skyrocketed to $28.0 billion.

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In case after case, self-confidence and fearlessness save the day for members of the Forbes 400. But it also helps if they are obsessed with their vision. Take, for example, the case of shipping magnate Daniel Ludwig. Born in 1897, Ludwig started out at age 19 with a $5,000 loan that he used to buy and convert a paddle steamer into a barge. Later he moved on to chartering and eventually building tankers, becoming the owner of the fifth-largest tanker fleet in the United States by the end of World War II.

One of America's wealthiest men by the 1960s, Ludwig was convinced that the world was headed for a food and fiber shortage, especially paper, so he embarked on a scheme of enormous ambition: to build a paper mill, and establish a buffalo farm and a rice plantation in a remote part of the world.

Ludwig focused on Brazil, where he bought more than 6,000 square miles of Amazonian rain forest, an area about the size of Connecticut, for $3 million in 1967. The Jari Project, as it was known, was one of the most grandiose and ill-fated schemes the world has ever seen. Ludwig built a port and a 26-mile railroad. He also built 3,000 miles of roads, as well as towns and settlements that housed 30,000 people by 1982. When Ludwig ran into difficulties building a 17-story pulp mill and power plant, he had them built in Japan and towed 17,000 miles across the ocean.

But the Amazon was a force Ludwig could not control. The trees he selected for the paper mill either died or grew too slowly in the jungle. The rice plantation failed. As if the Amazon weren't trouble enough, Ludwig came under increasing pressure from Brazilian nationalists who were suspicious of a foreigner's vast acreage and business in the jungle, and by a government bureaucracy that hampered him at every turn.

Finally, Ludwig gave up, selling Jari to a pool of government-aided Brazilian companies for $280 million. In his prospectus for the sale, Ludwig claimed to have spent more than $850 million on the project. Yet despite his huge losses with Jari, Ludwig still topped that first Forbes 400 in 1982 with a net worth of $2 billion, thanks to his shipping interests and other real estate.

Since so few members of the Forbes 400 have ever filed for bankruptcy protection, it's reasonable to surmise that those who do use leverage take very few risks they cannot afford. Jerry White of the Caruth Institute for Entrepreneurship at Southern Methodist University's Cox School of Business claims that in his 30 years of examining entrepreneurial careers, he has come to the conclusion that entrepreneurs who are successful in the long run are actually moderate risk takers when their leverage is set against the scale of their wealth.

Daniel Ludwig, of course, lost hundreds of millions of dollars on his failed Jari Project, yet he was still left with a considerable fortune. If Warren Buffett gambled $1 billion in 2006 and lost it all, his net worth would still have been $45 billion. "If you talk to these people off the record," says White, "then they will tell you that they only lose in proportion to their ability to recover."

Look back at those card games favored by the Forbes 400: poker and bridge. These are games where skill has as much--if not more--to do with winning than luck. "Gamblers are losers and hedgers are winners," says White. "And entrepreneurs instinctively understand that in their gut."