I should be a millionaire right now. Unfortunately, I'm not. As Marlon Brando once said, "I coulda been a contender."

Mexico's Carlos Slim Helu, who owns controlling interests in Telefonos de Mexico (NYSE:TMX) and America Movil (NYSE:AMX), is worth some $60 billion, having recently surpassed even perennial top dog Bill Gates and his Microsoft (NASDAQ:MSFT) fortune. I'm worth considerably less. How did that happen?

It's simple: I did nothing. For almost 20 years after graduating from high school, I did nothing. I missed out on Microsoft's 900% return. I didn't buy any stocks at all.

Rolling the dice with stocks
You see, I was brought up believing the stock market was a crapshoot. I believed I had a better chance of making a killing by going to Atlantic City and throwing it all on black at the roulette tables than securing a sound financial future by investing in America's best companies.

So instead, I bought fancy cars, had a big house with a mortgage that strained my ability to pay for it, ran up my credit-card debt to buy the things I wanted -- not to mention the things I needed -- and put very little aside in savings. I was fortunate in that I had a pretty decent-paying job with good health benefits. I could have been putting money aside, but chose not to. I was living the good life.

Fast-forward 20 years and there I was: 37 years old, recently divorced, driving a beater car, $50,000 in debt, and looking at roach-infested rooms to sleep in. And even though I still had that decent-paying job, which was paying me even more handsomely than it had before, I still had no savings to speak of.

Now look at Carlos Slim, Bill Gates, or Warren Buffett. While the comparisons may not come easily, the differences are pretty stark. Where I was living a profligate lifestyle more suited to the millionaires, the billionaires were living far more modestly.

Inside the millionaire's mind
Helu buys ties in the stores that he owns. Gates focused solely on growing his business. And Buffett still lives in the modest home he bought decades ago. In fact, the surprise bestseller The Millionaire Next Door points out that the "typical millionaire" is a homeowner who has owned his or her house for more than 20 years, wears inexpensive suits, and owns and drives American-made cars that are more than just a few years old. Not only that, but these millionaires are prodigious savers who have accumulated a "go-to-hell fund" that would allow them to live without working for 10 years or more.

They also invest. On average, the typical millionaire invests about 20% of household income each year. That sounds a lot like Carlos Slim, who bought Telmex for pennies. It sounds a lot like Warren Buffett, who found American Express (NYSE:AXP) and Washington Post (NYSE:WPO) attractive and inexpensive when others didn't. They invested in companies that were the best at what they do. They did it cheaply, and they did it regularly.

The greatest source of wealth -- ever
That's why I'm not a millionaire today. I spurned the greatest wealth-making vehicle there is. Better than gold. Better than real estate. Better than any other investment. It is in stocks that we will find the greatest wealth-creating opportunities.

Instead, I put my money into things that lost value, depreciated soon after I drove them off the lot, or satisfied some immediate-gratification urge with little respect to long-term worth.

Fortunately, I've recognized the error of my ways. Today, not only have I paid off most of my debt (I did just buy another house), I put money aside regularly, and I invest. My stocks might not be the ones a Slim, a Gates, or a Buffett would buy, but I think they've got potential to help me finally reach that million-dollar goal.

Going 10 rounds or more
In reality, it doesn't matter exactly which stocks I own, but rather that I own them. I'm always scouring the market for new opportunities, new companies to rise with. I might have squandered my early years not making my millions, but I'm determined to ensure that my later ones are not so barren.

When it comes to investing, we need to do it early, do it often, do it always -- through good markets and bad. When the bell rings, we won't have to say we "coulda been a contender."

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Fool contributor Rich Duprey finally did buy some stocks, but he doesn't have a financial position in any of the stocks mentioned in this article. You can see his holdings here. The Motley Fool has a disclosure policy.