Estimates suggest the average investor now holds a stock for less than seven months, down from eight years in 1960. So the fact I recently sold a currency position I had held for more than four years probably makes me somewhat of a throwback. Still, as we always point out, it s the holding, not the trading, where the real money is made.

Average Holding Period for NYSE-Listed Stock

Source: Loyalty Shares Presentation by Patrick Bolton (Columbia Business School) and Fredeeric Samama (Amundi Asset Management).

Yet despite all the swapping going on, many investors actually struggle with making changes in their portfolio. When we ve held a position or indentified with a particular market outlook for so long, it can often be difficult to move on. After all, we ve invested not only our money, but our ego, time and mental energy. I held that particular currency trade longer then my entire high school career. I spent hours researching it over the years, not to mention the dozens of hours at a bare minimum I spent watching it. Selling it, even with a substantial profit, wasn t easy.

But investments are not people. They re not girlfriends, family members or close confidants to whom you owe any loyalty. When it s time for a change -- whether it's because of a shift in your portfolio, conviction or investment goals -- the only approach is that of a hired assassin: Do it quickly, move on and don t look back.

Even then, there are a few common pitfalls that can trip up investors of any size:

Selling One Stock Doesn t Necessitate Buying Another

The decision to exit one position is totally separate than the choice to invest in something else. Yet because we re so accustomed to having money at work, oftentimes upon exiting one trade, we immediately scramble to find something anything else to buy.

It s especially true when we re selling a stock at a gain. Because it feels good to take a profit, overconfidence can tempt us to immediately try to repeat a previous success.

Resist the trap to immediately swap the proceeds from one sale into another exposure simply to have money at work. And if you do opt to take a new position, as a disciplined investor, you should once again start with an initial trading unit, ideally between 2% and 5% of your portfolio, not simply the arbitrary proceeds of one sale.

To sell shares of a gold stock like Goldcorp only to buy another precious metals exposure like Barrick Gold or PowerShares DB Gold doesn t make much sense, given how closely correlated the two securities are. Yet after being successful in one sector or industry group for a long period of time, we often don t know where else to turn.

That was the case after the 2000 tech downturn when, even after taking losses on dot-com era blow-ups like Webvan.com, many investors instead opted for stable but similar names like Cisco and Microsoft. While they might not have dissolved like TheGlobe.com, the fact they too were technology stocks meant missing out on ideas like real estate and commodities, both of which were just on the cusp of new multi-year bull runs.

So when exiting one trade, I ll often challenge myself to look outside my comfort zone into new areas where I had no exposure or even interest. Because markets are always changing, the idea is to broaden your world view to include asset classes or strategies you hadn t previously considered. Did the same investors who once held large positions in America Online or Nokia in the late 1990s really think they d be touting the virtues of platinum or dividend-paying stocks today?

Cut the Cord

Finally, after owning a particular stock or asset for a long period of time, we often make the mistake of continuing to follow it even after we ve exited the trade. Investing is, after all, an emotional business, and like the heartbroken lover stalking his ex on Facebook, it can be surprisingly difficult to let go.

Yet that s exactly what works best. Regardless of what happens with XYZ, continuing to track it invariably leads to losses even worse than a broken heart.

If the asset continues to climb even after we ve sold, we ll often berate ourselves for missing the move or, even worse, end up chasing it higher by repurchasing at a higher price. If it falls, we re tempted to jump back in and play a potential rebound, which by definition is among the most reckless maneuvers of them all. All the while, the prior investment experience colors and distorts our objectivity regarding round two.

So after selling a stock, I will take it off my screen, at least for a little while, as to avoid the second-guessing that comes along with watching a previous holding continue to climb or fall. There are thousands of publically traded companies, funds and market strategies from which to choose. For your sanity, once you ve moved on with your money, you re best served by moving on with your attention, as well.