According to data from TowerGroup, more than half of all U.S. investors make fewer than five trades per year. At the opposite end of the spectrum, just 0.3% identify themselves as day traders who make more than three trades in a day.

You've probably heard that trading is hazardous to your wealth, and you follow the Foolish principle of buy-and-hold investing set forth by Buffett, Lynch, et al. Good for you -- you're sticking to your guns, keeping taxes and commissions low, and trying to beat the market.

But ...
When you're buying stocks both infrequently and with the intent to hold them for extended periods of time, you probably sweat the buy and sell decisions in a big way.

That's why we can't underscore enough the importance of keeping a watch list. Every investor needs a watch list -- and not just a few tickers scribbled on an envelope. We're talking about an unwieldy, expansive, and possibly color-coded endeavor.

Make every purchase count
At our Motley Fool Hidden Gems small-cap service, we add companies to our watch list every month in addition to making two formal recommendations. For the companies that go on the watch list, either we want a better price, or we want to see some sort of change in the business.

From there, a company may become a recommendation if the business improves or if it sees a sudden and substantial drop in share price.

Enough introduction
Hornbeck Offshore Services (NYSE: HOS) went on my (Tim's) watch list in May 2006, after I listened to a presentation by Todd Hornbeck, the company's CEO, in New Orleans.

Here was a company making money hand over fist. As the operator of the most technologically advanced fleet of offshore supply vessels (OSVs) for large energy companies, the company possessed an important competitive advantage and was well positioned to benefit from a long-term rise in energy prices. Finally, the CEO owned nearly 2% of shares and had his name on the door.

The stock only made it to the watch list, though, because I was worried about price.

A bit more background
Hornbeck was then trading for about 20 times earnings, and its shares had more than tripled following its 2004 IPO. Even without crunching the numbers, it was clear that the stock had gotten ahead of itself.

After all, energy is a cyclical industry, and 2006 was a boom year. What's more, Hornbeck was seeing even greater demand for its ships in the Gulf of Mexico because of damage wrought by Hurricane Katrina. The stock was priced as if this operating environment would continue indefinitely.

It didn't
Fast-forward to Jan. 11, 2007. Hornbeck stock dropped 22% in a dayafter the company substantially lowered fourth-quarter guidance and announced that it could drop its 2007 guidance by as much as 20%.

Of course, now our interest was piqued. Hornbeck came off the watch list and onto the whiteboard for more research.

But we didn't like what we found.

Operating OSVs is an extremely capital-intensive business. As the old saying goes, "The two happiest days of a boat owner's life are the day he buys the boat and the day he sells it." And although Hornbeck was a very profitable company, it did not spin out a lot of free cash flow. And with day rates dropping, insurance and maintenance costs rising, and some volatility in the energy sector, it wasn't clear that Hornbeck (1) wouldn't fall any further, or (2) would see sufficient returns to send the stock back up. Continued...