On June 7, I watched the Internet video feed from Las Vegas as Mike “The Mouth” Matusow pocketed $266,503 by winning the 13th event in the 2013 World Series of Poker.

Matusow has won nearly $9 million playing tournament poker, and I’ve studied nearly every hand he has ever played. I even sat next to his mother the night he won $1 million in the Championship Event of the 2005 World Series of Poker.

During his recent tournament, Matusow seldom had the lead. But he played a disciplined game. He folded many hands while his opponents wasted chips, chasing after hands they didn’t have the odds to win. Matusow’s patience and premium hand selection over the course of the three-day event were rewarded with the first-prize gold bracelet.

I’ve played poker for more than a decade. I’ve had the opportunity to study — and go up against — some of the best professionals in the world. I’ve seen players amass big leads in a tournament, only to turn right around and give every chip back. In my experience, both as a poker player and an investor, the decision to not play a mediocre hand can be the most profitable decision you can make.

It’s easy to spot an inexperienced player at a poker table. He’ll be the guy who plays nearly every hand. He’s probably grown up watching televised poker, where folded hands are edited out to highlight the relatively few contested hands. In his limited view, he believes by playing more hands, he has more chances to win. He has no idea how many hands he’ll lose before he gets lucky.

I want this guy at my table for as long as his money lasts.

Inexperienced investors tend to own too many investments. They mistakenly believe that more is better. For every high-quality stock that outperforms the market, they have three underperformers preventing them from maximizing their profits. They might even own stocks with a low probability of making a profit just for the sake of diversification.

When you own dozens and dozens of stocks, it’s hard to keep track of how each individual company is performing. Most investors get overwhelmed by the task and give up, hoping it will all work out in the end. Once I started playing poker and learned this lesson, I trimmed the number of holdings in my personal portfolio. I got rid of my mediocre performers and focused all my attention on the remaining high-potential holdings.

When I designed Stock of the Month, I kept this important lesson in mind. While I research dozens of investments each month, I invest in only one — the single best opportunity.

I only keep 12 stocks in my portfolio at a time. Every month I buy a position, I sell off my holding that holds the least promise going forward. This way I can watch over each investment like a hawk.

Even famed investor Warren Buffett swears by rigorous selectivity, saying, “It’s crazy to put money into your 20th choice rather than your first choice.”

So far, Stock of the Month’s disciplined and selective strategy has paid off. Of the dozens of closed trades executed in my model portfolio, nearly 85% have been winners.

As it turns out, in poker and investing, “less is more.”

P.S. — Most people don’t like to equate investing with gambling, but as I just explained, using the skills I learned on the poker table in my Stock of the Month newsletter, I’ve picked winners that have returned 50% or more. Though getting a track record like that wasn’t easy, I use an incredibly simple strategy. To learn more about it, click here.