I think it’s the most important tool an investor can use.

In my Stock of the Month advisory, it has certainly helped me out. Eighteen of my 20 closed trades are winners. I wouldn’t be anywhere near that mark without this tool.

And the best news is it doesn’t cost a thing. The tool is common sense.

Now I’m not trying to downplay the importance of research, or trying to make investing sound as simple as tying your shoes. If it were that easy, then we’d all be Warren Buffett.

But I think you’d be surprised at how far using common sense can get you…

Let me give you an example.

Oil, cotton and food prices are very high right now. So I’m less interested in companies that have to spend large chunks of money on these commodities. That means the apparel and restaurant sectors aren’t in play for me right now. Unless these companies can pass on higher costs to their customers, it’s going to kill their profits.

You don’t have to have a doctorate degree to understand this. It’s common sense.

And when you’re investing, knowing what you don’t like is as important as knowing what you do like. It saves a lot of time and keeps you from being overwhelmed.

I see a lot of investors with massive numbers of investments in their portfolios or who attempt complicated trading strategies. Eventually they get overwhelmed. They can’t effectively track what they own. Trades go unexecuted. Brokerage statements end up, unopened, at the bottom of their desk drawers. And most importantly, their portfolio performance suffers.

I think this is one of the reasons Stock of the Month has resonated with investors. Keeping things simple seems like a no-brainer in a market that gets more complex every week.

And I’m not alone in this “common-sense” approach.

Buffett himself is one of the greatest proponents of keeping things simple. That’s why, even with a stock portfolio of more than $50 billion, Berkshire Hathaway’s (NYSE: BRK-B) top 10 holdings make up more than 90% of the portfolio. As Buffett says, “If you have a harem of 40 women, you never get to know any of them very well.”

So where does this approach point my investing now? Well, you don’t have to read between the lines to know this summer is shaping up to be slow on the economic front… Ben Bernanke has said so himself. That’s in addition to problems in Greece and the debt-ceiling debate here in the United States.

Common sense tells me it’s time to get defensive. But I’m not tempted by the traditional defensive sectors, especially health care. Many of these companies have tepid growth outlooks.

Instead, I’ve been researching companies that maintain the health of computer networks.

When computer networks slow or falter, companies lose money. If you’re a big online retailer like Amazon.com (Nasdaq: AMZN), every lost hour of access to your site costs roughly $600,000 of lost revenue.

In the case of network security breaches, a company can also incur costs associated with customer account identity theft. That was the case for Sony (NYSE: SNE), which has spent roughly $170 million to rectify a recent hack attack involving customer account information on its online-gaming network.

Action to Take–>  Even if the economy slows this summer, companies will continue to invest in the health of their computer networks. And that’s good news for the stocks that can deliver in this arena.

It’s just common sense.

P.S. — Stock of the Month is radically different from most newsletters. It is as simple as investing gets — just one pick per month. But the biggest difference? I actually buy each recommendation for the newsletter’s $100,000 portfolio. After all, if I’m going to recommend you buy something, shouldn’t I have to do the same? It’s just common sense.

To learn more about the advisory, be sure to visit this link.