In theory, the market is pretty efficient. According to prevailing Wall Street wisdom, rational investors will quickly take advantage of any mispricing, thereby bidding firms back to their true value. That's all fine on paper, but it relies on several assumptions that are just plain false. By learning how and where the academic theory gets lost in reality, you can take advantage of the system for your own personal financial benefit.

The irrational advantage
Probably the biggest hole in the theory is that it assumes that investors are always rational. For that to hold true, investing decisions would largely need to be made in a vacuum. In reality, most people invest for a purpose, not just for academic curiosity. We all want better lives for ourselves and our families. Maybe we're saving for college. Maybe it's a comfortable retirement we're after. Whatever the reason, investing is a means to an end, and not an end unto itself.

If your portfolio gets shellacked, it's not just an abstract paper loss. It's real money that may very well translate to an unpleasant change in your long-term plans. No matter what the academic theories claim, invested money has real-world consequences that change people's behavior away from the purely rational.

Fear and greed
Because of this, emotions play a huge role in people's actual investment decisions. By far, fear and greed loom the largest. When a stock is going down, people's natural tendency is to get scared. After all, it's their money on the line, and they have plans that will fall apart if the cash isn't there when it's needed. As such, folks tend to want to sell a falling security to preserve whatever remains of their capital.

What this means is that selloffs are often far more dramatic than they should have been. As a result, you can snap up shares for far less than they're truly worth. After all, it's called a panic sale for a reason. Just like a department store trying to rid itself of "scratch and dent" merchandise, fear sometimes causes the stock market to offer incredible bargains on companies that are only slightly damaged. As a value-focused investor, you can take advantage of this mispricing to profit.

On the flip side, when stocks are performing exceptionally well, investors tend to want to pile in on the action. Just as fear sends people running from a stock heading down, greed compels them to buy one that's rising. The resulting buying frenzy frequently drives a company's stock dramatically higher than it's truly worth. Unfortunately, just as everyone wants to purchase, the stock becomes its most dangerous. At a high enough price, there's nothing but hope supporting the stock. As a value investor, that's your opportunity to sell or your cue to stay away.

The consequences
The upshot of all this emotionally driven buying and selling is that stocks tend to trade both well above and well below their true worth from time to time. You can see this by looking at something that I like to call the emotion factor. In essence, it's a comparison between the 52-week low and high prices of a company and its expected five-year growth rate. The higher the price changes compared with the growth rate, the more likely that emotion is involved.

The logic behind the emotion factor is this: If the market always efficiently reflected the future, then stocks would always be priced at their true value. Consequently, any growth in the stock should be fueled only by growth in the underlying business. The larger a stock's movement variation with respect to its expected growth rate, the less likely that its price will always precisely track its true worth. Here's what it looks like, in practice:


52-Week Low

52-Week High

Low to High Fluctuation

Expected Growth

Emotion Factor

Advanced Micro Devices (NYSE:AMD)












ExxonMobil (NYSE:XOM)






Altria (NYSE:MO)






GlaxoSmithKline (NYSE:GSK)












Citigroup (NYSE:C)






Data provided by Yahoo! Finance

Topping this list are the perennially feuding microprocessor manufacturers Intel and Advanced Micro Devices. Their regular battles back and forth over technical supremacy lead to regularly shifting investor sentiment and market share changes. When the lead shifts between the two, the market often reacts as though the company which had been knocked down would soon be knocked out -- permanently. The reality is that the global PC market is big enough for at least two microprocessor companies. As long as these two keep leapfrogging each other, both will likely survive for quite some time.

On the flip side, at the bottom of the list is international money center bank Citigroup. A global titan in its industry and a master at financial management, Citigroup is generally considered a boring stalwart and a paragon of stability. Short of a major global financial meltdown, it's hardly the kind of company where emotions would routinely rule the day.

How to profit
Of course, the emotion factor alone won't tell you whether a company is currently over- or underpriced. It will, however, tell you how much the firm's stock has recently moved independently of the expected changes in the true worth of the business behind that stock. The bigger the moves are, the better the chances that the market overreacted because of excessive fear or greed.

If the culprit is excessive fear, you can pounce and profit. It was during just such an episode that Motley Fool Inside Value lead advisor Philip Durell picked Intel this spring. Advanced Micro Devices still had the technical upper hand prior to Intel's public unveiling of its new generation of processors. As such, Intel was being largely written off as a has-been and an also-ran. Such pessimism about the company's future provided just the discounted price that value hounds such as Philip seek.

As Intel regained the technical lead, its shares have held up far better than its archrival's, in spite of the general panic currently hitting many companies in the semiconductor industry. While Intel hasn't quite rocketed to the moon, it has been a stellar example of how buying when there's excessive pessimism in the air is a great way to follow Warren Buffett's famous Rule No. 1: "Never Lose Money."

The Foolish bottom line
In the stock market, there's real money on the line, with real consequences to real people. As such, emotions run high. If you learn to recognize when investors' emotions have taken control of a stock, you can use that information to your advantage. Simply buy when a sour mood has knocked a company's shares to well below their true value, then sell when a jubilant one has ratcheted them to well above their true worth.

Are you ready to take advantage of the market's emotional roller coaster? Join Inside Value and learn how to uncover other opportunities to profit from the market's bouts with excessive pessimism. Want more information before committing? A 30-day free trial will cost you nothing more than your time.

This article was originally published on July 10, 2006. It has been updated.

At the time of publication, Fool contributor and Inside Value team memberChuck Salettaowned shares of Intel. Intel is an Inside Value selection. GlaxoSmithKline is an Income Investor choice. The Fool has adisclosure policy.