Imagine this simple scenario...

Say you own two stocks. You bought each at $50 a share. Over the course of your investment, one has risen to $75 per share. The other has fallen to $25.

Suddenly, you and your spouse decide you need to raise money for something immediately. Perhaps a car you've wanted is on sale at the local dealer, or a cabin on a lake where you want to retire is suddenly on the market. You decide to sell one of your investments. But which stock do you sell?

If you're like most people, you choose to "capture" your gains... sell the $75 winner and keep holding the $25 loser. You may think the losing stock seems to have more upside potential, and you've probably been waiting to "get even" on the position...

It's a nearly universal impulse... but it's a terrible investing choice.

Today, I'll show you how to avoid this tempting mistake with a simple strategy...

We love to sell our winners too soon and ride our losers too long. A slew of behavioral finance studies shows it. One, by University of California at Berkeley professor Terry Odean, found investors are almost twice as likely to sell a winning stock as they are to sell a losing stock.

Worse, in the study, it turned out the winning stocks that investors sold subsequently outperformed the losing ones they were still holding.

When most people buy a stock, they worry about what to do if it falls. But dealing with rising stocks presents an equal challenge.

This blind spot in the human psyche regularly worried Peter Lynch...

Lynch is an investing legend. He averaged 29% annual returns over the 13 years he ran Fidelity's Magellan Fund. He was also an eternal optimist when it came to buying stocks. His analysts joked that he "never met a stock he didn't like," and his fund swelled to more than 1,400 holdings.

Of course, no individual investor should try to manage even 140 positions, let alone 1,400. But the point is... Lynch had a different outlook on the market than most folks.

Once an investment shows a little gain, fearful ideas permeate our thoughts. Any little bit of news – good or bad – seems like a reason to lock in gains.

But as Lynch said...

We've been warned that a rise in oil prices is a terrible thing and a fall in oil prices is a terrible thing; that a strong dollar is a bad omen and a weak dollar is a bad omen; that a drop in the money supply is cause for alarm and an increase in the money supply is cause for alarm.

There's no single rule that will tell you when to sell. That's because there's no rule that tells you when to buy. So my advice is this...

The strategy for selling is determined by why you bought in the first place – and should be determined at the time of your initial investment.

When you buy, it's critical to know exactly what you expect to get out of the investment and what would lead you to sell. Here are three keys that help...

1. Write down WHY you bought it.

2. Write down WHEN you'll sell it.

3. Review your investment at least once a year (but preferably every six months).

One trick I use to make sure I stick with my discipline is to ask myself whether I'd buy more right now or recommend it to friends or family members. If the answer is no, it's probably time to sell.

If I'm really worried that I'm making a mistake by selling, I remind myself that I can always open a new position after a 30- or 60-day break. There's nothing magical about this time frame. It just serves as a cooling-off period for my emotions. Most likely, a good investment will still be attractive at that point. And in many cases, I've found better opportunities by then.

That's also why at Stansberry Research, we often recommend 25% trailing stops with our stock investments... which means we sell if the stock falls that far from its high point during our holding period.

There are plenty of valid sell signals you can use to cut short your losers. But trailing stops are a simple, easy-to-understand way to eliminate your emotions and get out of losing positions before they get too large.

The next time you wonder if you should take some money off the table, consider whether you're making this common mistake. And make sure you use these tips from the moment you buy... It's a far better way to plan your investments.

Here's to our health, wealth, and a great retirement,

Dr. David Eifrig

Editor's note: This is exactly why our friend and colleague Dr. Richard Smith just revealed a unique way to know when to sell each of your stocks. It's a system designed to take emotion and biases out of the equation... regardless of what the market is doing. To find out how it works, watch the replay of his recent online event right here.

Investing gets complicated fast... That's why having a clear plan for when to sell is important. And it's also vital to understand what matters when buying your next stock...

Market Notes

IT'S A BULL MARKET IN PACEMAKERS FOR AN AGING AMERICA

Today's chart demonstrates a key investment theme from our colleague, Dr. David Eifrig...

Baby Boomers are America's largest generation. And as they enter their golden years, many Boomers will need more help to stay healthy. Here at DailyWealth, we've tracked strong performances from stocks participating in this big trend, including health insurers, medical-building owners, and drug developers. Today's company fits the same idea...

Boston Scientific (BSX) is a $55 billion medical-device manufacturer. It makes pacemakers, stents, and catheters. A large portion of its business works on treating heart conditions. And in an aging America, demand is increasing for Boston Scientific's medical innovations... In the most recent quarter, the company's sales grew more than 6% to $2.6 billion. That figure includes sales growth in all three of its segments.

As this chart shows, BSX is riding this tailwind. Shares have tripled since early 2014, and they're up about 50% over the past year alone. It's more proof that Baby Boomers are creating a boom for health care stocks...