"A bird in the hand is worth two in the bush."

I'm sure you've heard this saying before. The lesson it imparts is that it's better to settle for what you have than risk everything in an attempt to gain more. That may work in some situations, but not if you're investing for big long-term gains. To hit on the next multibagger, you need to:

  1. Find a great stock.
  2. Give it time to fulfill its potential.

The first part is hard enough, but the second may be harder. When a stock appreciates by 50% to 100%, it's tempting to sell and lock in gains. In fact, there are plenty of investors who, after a stock doubles, sell half so they can say they're now playing with "house money." Unfortunately, both approaches can lead to huge losses. Yes, losses.

Learn from the worst
Take my biggest loss, for example. In January 2005, I had been doing some research on SanDisk (NASDAQ:SNDK) and realized that a dominant name in an emerging industry -- in this case, flash memory -- was undervalued relative to its peer group. Even better, I calculated it to be a $60 stock. So I picked up some shares at $24.75.

But over the next few months, the stock just sat there. Sat there! Had my research been wrong? Finally, SanDisk jumped to $32.25 after a good second-quarter earnings report, and I decided to pocket my 30% return before the stock returned to the $20s.

That's been the most painful 30% gain of my life. By early January 2006, SanDisk surged to a high of $79.80, and I had to swallow a 190-percentage-point opportunity loss.

Learn from the best
Fool co-founders David and Tom Gardner and their team at Motley Fool Stock Advisor are loath to sell great stocks -- although they have done so and later regretted it.

One of those lessons came from Tom's selection of Whole Foods Market (NASDAQ:WFMI) in 2002. A year later, the stock had gained 72% for the portfolio, and Tom, believing the stock was sitting on a tenuous valuation, captured the gain and sold the position. The stock continued to grow, however; it gained an additional 96% after it was sold.

The Whole Foods lesson paid off a few months later, when Tom decided to hold onto Quality Systems (NASDAQ:QSII) -- even after it had returned 154% in a year's time. He sensed that there was still a wide market opportunity for digital medical records. And that was smart. The stock has now returned more than 560%.

A stock that had a good year can always have another one. Indeed, cutting winners short is one way that many individual investors hurt their returns. Sensing that energy prices were peaking in the summer of 2005, many investors believed that the run in the sector was nearing an end. Yet those who bailed continue to miss out on good returns.

August 2004 to
August 2005

August 2005 to
August 2006

Total Return

Valero Energy (NYSE:VLO)

123.6%

62.0%

262.3%

Marathon Oil (NYSE:MRO)

58.5%

51.9%

140.7%

Kerr-McGee (NYSE:KMG)

56.3%

72.2%

169.1%

Tesoro
(NYSE:TSO)

73.7%

51.7%

163.4%


The Foolish final word
If you truly believe in your original assessment of a stock, then let your winners run. While there will always be a few bad picks in your portfolio, your winners can more than make up for them if you hold onto them patiently and optimistically.

Need help picking some winners that are worth keeping around? Give our Stock Advisor newsletter a go-round for 30 days, free of charge. Tom and David thoroughly explain all of their picks as well as the drivers that make them worth holding for the long run.

Todd Wenning does not own any shares of companies mentioned in this article. Whole Foods and Quality Systems are Stock Advisor picks. The Motley Fool has a disclosure policy that even Chuck Norris couldn't get out of with a roundhouse kick.