Let's imagine that The Motley Fool gave you $100,000 to invest in your favorite stock two decades ago. We agree to split the winnings after 20 years. Why? Because you're smart, you look like a million bucks, and you've got no detectable personal hygiene issues. We like you. We believe in you.

The year is 1986. A hundred thousand bucks has your nerves on edge, so you pop a Lionel Richie cassette into your Walkman ("Say you, say me ...") and cruise to the local cinema to catch the matinee of Mickey Rourke's new flick 9 1/2 Weeks. (Interesting choice.) Three hours later, kicking past a strip mall of Thom McCann, Arthur Treacher's Fish & Chips, Bradlees, and Crazy Eddie, you have an idea.

You'll ask Gramps for his favorite stock, then you'll ask your cousin Marilyn Meeker for hers. Gramps was a banker for 41 years. Marilyn's getting a business degree. You'll get two different perspectives. Good plan.

Two roads diverged
Over finger sandwiches and Canada Dry on the patio of your grandfather's country estate, he raises a crooked index finger to the sky and says simply, "Eastman Kodak (NYSE:EK). The stock's a stalwart. All in, with dividends reinvested and splits, it's up 10 times for me over the past 20 years. A nice, conservative pick."

A few days later, hammering away at a Galaga machine at the local arcade, your cousin rattles on about a small-cap stock. "It's a new issue," she says. "Oracle (NASDAQ:ORCL). Its software helps businesses store customer data. If you've got 20 years, go with a solid small company like Oracle. It's in a great industry and its founder and CEO owns a ton of stock."

After a few hours of reflection, you rotary-dial your Motley Fool contact with this directive: "For the next 20 years, I say put that $100,000 into _______."

Which?

The 20-year mark
Since 1986, Eastman Kodak has risen about 50% (excluding dividends) for a miserable yearly return of 2%. Against that, Oracle is up 60 times in value. With Kodak, your $100,000 has turned into $150,000. With Oracle, it's swelled to $6 million. That's the difference between thousands and millions for long-term investors.

At Motley Fool Hidden Gems, we search for these multimillion-dollar opportunities by analyzing promising small-cap growth stories like HealthExtras (NASDAQ:HLEX), Rimage (NASDAQ:RIMG), and Buffalo Wild Wings (NASDAQ:BWLD), while avoiding overgrown giants like General Motors (NYSE:GM) and AT&T (NYSE:T).

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Tom Gardner is co-founder of The Motley Fool and heads up the Hidden Gems newsletter service. Tom does not own shares of any companies mentioned in this article. Buffalo Wild Wings is a Hidden Gems recommendation. The Fool isinvestors writing for investors.