If some supposed investing guru offers to show you, for a fee, how to get rich in a few weeks or months, we hope that you'll turn and run away. Unfortunately, some Americans are doing the opposite. They're buying self-published make-millions books, attending expensive seminars, and calling 900-numbers for financial guidance.

A man named Wade Cook, for example, has spoken of earning 20% to 40% returns -- monthly. Let's do a little math and see how realistic this is. If you take a single dollar and compound it at 20% monthly for 15 years, you'll have $179 trillion. Last time we checked, that was more than seven times the gross domestic product of the entire world, more than the total market value of all goods produced and services rendered globally in an entire year. This kind of result from investing a single dollar should seem a little unrealistic.

If these financial gurus were using their own systems to invest their own money for any significant period of time, they would long ago have appeared on lists of the richest Americans. Indeed, they'd have purchased most of our solar system. Instead, they appear to be making most of their money from selling their products, not from their stock market strategies.

Since Cook appears to know how to make billions, we find it surprising that he spends any time offering investing seminars that cost several thousand dollars. A few years ago, his "Wall Street Workshop" cost a whopping $5,695 and his "Zero to Zillions" audiocassette tape set was $1,295. At the same time, Cook's company was a penny stock, trading for about 25 cents per share with a measly total market value of roughly $15 million. It was reporting net losses instead of net profits.

Fast-forward to now, and the company's website states: "Wade Cook Financial Corporation (WCFC) has filed for Chapter 11 Bankruptcy and is no longer providing seminars for new or old customers." Sadly, the website also pitches a new company selling new seminars.

While the Fool recommends investing in stocks and holding for decades, many investing gurus urge you to use money you've borrowed for high-risk options trading. We generally try not to dabble in options, as they can (and often do) end up worthless. Also, investing with borrowed cash means that any mistakes translate into magnified losses. Gurus tend to rely heavily on predictions of short-term movements of stocks. We know that no one can consistently and successfully make such predictions -- even Dionne Warwick (as far as we know).

For the best way to accumulate wealth, look at two of America's greatest financial successes. Bill Gates grew wealthy hanging on to shares of his ever-growing Microsoft (NASDAQ:MSFT) stock. Warren Buffett, chairman of Berkshire Hathaway (NYSE:BRK.A), bought into great businesses and has held on to most of them. Both have publicly stated that among the qualities that have driven them to success, two stand out: patience and perseverance. How reassuringly Foolish.

To learn more about investing Foolishly, visit our Fool's School.

Longtime Fool contributor Selena Maranjian owns shares of Microsoft and Berkshire Hathaway.