Do you have difficulties knowing when to sell a stock? It's probably the single hardest thing for an investor to do well. Sure, finding great companies with undervalued stocks is tough, but selling them is even tougher. You'll never achieve the 20- and 30-baggers of the next decade if you unload a great business at the wrong time.

Even great money managers get bit by the selling bug, sacrificing hundreds of millions in profit, even billions, in order to lock in gains. Selling a slow-growing mega cap such as Bank of America or Citigroup is one thing (and may have saved you some heavy losses during the financial crisis), but you could wipe out the next home run stock if you try that trick with a fast-growing small cap.

Do try this at home
In early March, one of the great small-cap fund managers, John Laporte, retired. Working for the T. Rowe Price New Horizons Fund for 22 years, Laporte turned in an impressive performance. An investor who deposited money when Laporte took over, according to The Wall Street Journal, would now have a return of 7.8 times his money, net of fees. A similar investment in the Russell 2000, an index of small caps, would have grown to just 5.2 times the initial outlay.

A key component of Laporte's success was his ability to hold on to his winners, although admittedly even he sold some monster gainers way too early. Laporte held his stocks, on average, four years. But that figure understates the truth: New Horizons has held two-thirds of its top 20 largest investments for at least five years. On the other hand, the average small-cap fund flipped its portfolio every nine months.

The insanity of the average fund's actions is stark: How could you ever invest in the next household name if you hold a stock for just nine months? The renaissance of Apple (Nasdaq: AAPL) under Steve Jobs has taken years; the full flowering of Microsoft (Nasdaq: MSFT) under Bill Gates took a couple of decades. Can you imagine the millions you would have lost selling Microsoft just nine months after its IPO in March 1986? Now, Microsoft has absolutely dominant positions in Windows and Office, while Apple can turn lead into iGold.

And to get a sense of the capability and genius of managers such as Gates and Jobs takes time. Laporte confided to the Journal, "It often takes me years to get confident in the business strategy and the management team."

Two errors of commission
But despite its emphasis on buy-and-hold investing, New Horizons has two notable sales that cost billions in total. It held a public stake in Starbucks (Nasdaq: SBUX) from 1992 until 1994, when Laporte was convinced that a short-term move in coffee prices would hit the brewer's earnings. The fund manager took a profit on the shares, and then watched as shares grew 10 times more. That move cost the fund $200 million and ownership in the most recognizable name in coffee, one that is still growing rapidly and just initiated a nice dividend.

Another sale was much more costly. Before Laporte's time, the New Horizons fund purchased shares of Wal-Mart (NYSE: WMT) during its IPO in 1970. As the company outgrew its status as a small cap, the fund sold in 1983. Today its stake would be valued at about $14 billion -- twice what the fund as a whole is worth. The fund lost out on owning the world's largest retailer and its dominant competitive advantages, which were such a huge attraction to superinvestor Warren Buffett that he bought shares.

That's the power of buying and holding small caps. In fact, finance gurus Eugene Fama and Kenneth French discovered that 1 in 8 small-cap growth stocks become large each year. According to the researchers, these soon-to-be-large companies return up to 62% on average annually. Those are the types of gains that can turn you into an accidental millionaire if you hold on for the ride.

Where to begin
For those kinds of gains, focus on small caps that have high returns on capital and equity, such as the following:


Market Cap

P/E Ratio

Return on Capital (TTM)

Return on Equity (TTM)

Yongye International (Nasdaq: YONG) $395 million 15.2 27.1% 20.6%
Blue Nile (Nasdaq: NILE) $630 million 51.2 40.9% 44.6%
Female Health Co. (Nasdaq: FHCO) $155 million 44.5 28.7% 30.7%

Source: Capital IQ, a division of Standard & Poor's, as of Oct. 15.

Each of these stocks has had a bumpy ride over the last year, but the prospects for each are still very bright. Blue Nile has revolutionized the way you buy jewelry, becoming an online marketplace for the precious stuff. Female Health manufactures and markets the female condom, which does a brisk business overseas, especially in Africa. Yongye manufactures an organic fertilizer in China, and its business has been growing like it was sprayed with its own product.

Let's take a closer look at Yongye. The company is a new entrant to the stock market, and already its numbers are startling. Over the past two years, it has averaged sales growth of 119% annually, and earnings have clocked in 80% higher each year.

Of course, that type of growth has to slow. How could it be otherwise? But there's still a lot of opportunity here. The Chinese government is making a huge push (read: special treatment for ag companies) to use organic fertilizers in order to minimize environmental degradation and increase crop yields on relatively small portion of arable land. Yongye sits right at this nexus of opportunity.

The financials at each of these three small caps, as measured by returns on capital and equity, continue to look strong. Yongye and Female Health are up 13%-15% in the last three months, a nice gain, but with such strong fundamentals, why should you sell any of these stocks now? "Locking in your gains" in this case could mean you'll never score a two-bagger , five-bagger, or more.

Join us
Motley Fool Million Dollar Portfolio, our members have been able to benefit from small caps such as Yongye. We consistently search for and select from the strongest companies around – small, mid, or large caps -- and invest the Fool's own money in them. Our experts can add the super-power punch of small-cap investing to your portfolio, and we even tell you when to buy and sell (always before us).

If you realize that now, more than ever, is the time to own stocks in solid companies, consider joining us at Million Dollar Portfolio. If you'd rather see which companies have already made the cut, simply click here to enter your email address and learn more.

True to its name, The Motley Fool is made up of a motley assortment of writers and analysts, each with a unique perspective; sometimes we agree, sometimes we disagree, but we all believe in the power of learning from each other through our Foolish community.

Jim Royal, Ph.D. , owns shares of Yongye, Bank of America and Microsoft. Microsoft and Wal-Mart are Inside Value recommendations. Blue Nile is a Rule Breakers pick. Apple and Starbucks are Stock Advisor choices. Yongye and Female Health are Global Gains selections. Motley Fool Options has recommended a diagonal call position on Microsoft. The Fool owns shares of Apple, Yongye, Microsoft, and Wal-Mart. The Motley Fool has a disclosure policy.