Every stock trade involves a buyer and a seller. Both have access to roughly the same information, yet they choose to make polar-opposite decisions about a stock. If you want a shot at winding up ahead of the pack, you have to accept that fact.

To be successful, you must pay attention to what the person on the other side of your investment is thinking. Why is he selling when you're buying? Why is she willing to buy the shares you're trying to unload? If you can figure that out, you'll be light-years ahead of the competition.

Go! Fight! Win!
There's simply no such thing as a perfect investment. If there were, investors would soon bid up its price to the point where it was at least as risky as any other alternative. As a result, there are always two legitimate sides to any given analysis. To drive that point home, The Motley Fool runs a regular "Dueling Fools" feature, where analysts square off against each other on opposing sides of a stock.

While most investors look to buy stocks, the bear side of the duel points out the opposite side of the story -- reasons to consider selling shares. Quite often, the bear rightly predicts problems ahead -- ones that were visible to an outside observer, but not yet priced into the stock. As this chart shows, failure to heed a real warning can prove costly:

Company

Duel Date

Total Return
Since Duel

Return vs. SPDRs

Mentioned Warning Signs

Abercrombie & Fitch
(NYSE:ANF)

8/11/2005

16.8%

(9.1%)

Unstable comp store sales

JetBlue (NASDAQ:JBLU)

9/15/2005

-7.5%

(32.9%)

Airlines' tendency to go broke

Gap  (NYSE:GPS)

3/23/2006

6.7%

(10.7%)

Too much cost cutting, fading brand, falling cash flow

Disney  (NYSE:DIS)

6/22/2006

17.7%

(4.6%)

Valuation, overpaying for Pixar

UnderArmour  (NYSE:UA)

11/9/2006

1.7%

(8.0%)

Loss of first-mover advantage, valuation, no market clout

Since their respective duels, each of these companies has underperformed the SPDRs -- an exchange-traded fund that tracks the S&P 500. Worse yet, some of them have actually lost their investors a significant sum of money. The risks were well-known, in public, for all who wanted to pay attention.

Protect your money
Because there is no such thing as a perfect investment, and because there are always two sides to every analysis, any given stock will move up and down quite frequently. As our dueling bears have shown, even great businesses can easily become overpriced and headed for a fall. On the flip side, however, there are times when the worrywarts take full control of a stock and send it plummeting to well below its true worth. That's when value investors, like those of us at Motley Fool Inside Value, get interested in buying those same great businesses.

By always considering both sides of the story, it becomes that much easier to see those times when the market is driven to excess. Too much optimism? We sell. Too much pessimism? We buy. That's the simple truth to how we've managed to beat the market since our launch in 2004.

Make sure you're truly considering both sides of any potential investment. If this article has taught you to be skeptical enough not to blindly buy, congratulations -- you've already mastered the first step to becoming a successful value investor. As your prize, we'll give you a 30-day trial of Inside Value, free.

This article was originally published on Nov. 22, 2006. It has been updated.

At the time of publication, Fool contributor and Inside Value team member Chuck Saletta did not own shares of any company mentioned in this article. JetBlue, Gap, and Disney are Motley Fool Stock Advisor recommendations. Gap is also an Inside Value pick. UnderArmour is a Rule Breakers selection. The Fool has a disclosure policy.