I'm going out on a limb here with this story. I'm writing about how you, dear Fool, could make money by betting against Fool co-founder Tom Gardner.

Assuming I still have a job by the time I finish this story, you'll see how this isn't necessarily an indictment of Tom.

A Foolish experiment
Sitting in my cubicle as I went over the past performance on Tom's Stock Advisor scorecard, I started to notice something. It seemed to me that a lot of the stocks Tom had suggested selling were doing pretty well since his sell recommendations.

With that in mind, I went through all of his picks to see how an investor would have done had he or she invested in Tom's picks the day that he recommended selling. I had two requirements while sifting through his sells. First, I didn't include stocks of companies that were either taken private or bought out. Depending on the specific arrangements, it would be difficult to track these stocks against the S&P 500.

Second, I included only sell recommendations that occurred more than three years ago. As long-term, buy-and-hold investors, we believe in having a three-year time horizon at a minimum. We usually adhere to those rules as stock buyers, and we should use them to evaluate our sells as well.

These were the stocks left standing.

Company

Sell Date

S&P Since Sell

Stock Since Sell

Difference (Percentage Points)

Whole Foods (Nasdaq: WFM)

5/5/2003

60.5%

99.7%

39.2

Websense

7/21/2003

51.4%

140.8%

89.4

Sanderson Farms

8/20/2003

48.1%

137.6%

89.5

Kensey Nash

5/20/2005

21.0%

(9.5%)

(30.5)

Daktronics (Nasdaq: DAKT)

5/20/2005

21.0%

(5.0%)

(26.0)

Hypercom (NYSE: HYC)

5/20/2005

21.0%

57.4%

36.4

Regis

11/18/2005

14.3%

(63.5%)

(77.8)

Affiliated Managers

2/17/2006

10.4%

(0.2%)

(10.6)

Amerigroup

5/18/2007

(8.3%)

171.1%

162.8

Family Dollar

5/18/2007

(8.3%)

66.6%

74.9

Shuffle Master (Nasdaq: SHFL)

11/16/2007

(4.9%)

(22.3%)

(17.4)

Yahoo! (Nasdaq: YHOO)

2/1/2008

(1.2%)

(45.6%)

(44.4)

Resource Connection (Nasdaq: RECN)

4/18/2008

(0.9%)

(30.5%)

(29.6)

bebe stores

5/16/2008

(3.8%)

(42.3%)

(38.5)

Average  

15.7%

32.5%

16.8

*Source: Google Finance. Returns through June 6.

The decisions to sell several of these companies have turned out to be great calls, but I'm sure Tom wouldn't mind having a do-over on some of his older sell calls, including Websense, Sanderson, and Amerigroup (in which Tom recommended selling one of two positions he had).

A brilliant buyer … a not-so-brilliant timer
You may find this a harsh criticism of Tom, but I think there's another way to look at it: Tom is an excellent stock picker, but maybe not the best market timer.

I don't think he'd mind that distinction at all. In fact, when I asked Tom about what he's learned, here's what he had to offer: "The best investors set themselves up to use the stock market like a bank -- adding money at attractive prices and then never selling unless they need the money."

Tom's not alone
Truth be told, anyone who has been investing for more than a few years has some tales of "the one that got away." I bought Netflix (Nasdaq: NFLX) back when shares were about $65. When the price almost doubled in just three months, I sold a third of the shares in a knee-jerk reaction. Not only did I want to lock in some gains, but I was also worried about competition and content costs. With the stock now trading near $260, I'm left eating humble pie every day.

A Foolish takeaway
My mistake was that I sold based solely on valuation. Often, the best companies have scary-looking valuations for years -- as they soar ever higher. But don't let fear of the one that got away keep you from following and refining your investment strategy. For every stock you should have held onto, there'll be plenty that you'll be glad you sold.

Learn more about promising stocks with the Fool's special free report, "The Motley Fool's Top Stock for 2011." It'll tell you about an underappreciated stock that's on the cutting edge of its field. It's yours, for free.

Fool contributor Brian Stoffel owns shares of Whole Foods and Netflix. The Motley Fool owns shares of Whole Foods Market and Yahoo! Motley Fool newsletter services have recommended buying shares of Yahoo!, Whole Foods Market, Amerigroup, and Netflix, as well as buying puts on Netflix.

Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.