Stocks were up in 2006; that's hardly news. During the year, perhaps you sold to harvest a gain, or maybe to offset a few losses. I'm sure it wasn't an easy decision -- it never is. Now, as the new year has arrived and the markets continue to be strong, you wonder whether it's time to park some cash, build your 529 plan or buy depressed real estate. Selling is an emotional thing. Most of us are married to our investments, expecting something positive despite the most obvious and ominous outward signs. We hope, largely based on gut feel, that things will always get better. Further, many of us have been conditioned by past experience: One of our stocks climbs, meets and exceeds our goals, and we sell. Boy, does it feel nice -- for about two days. Then it goes on a tear, and we reflect miserably on the money left on the table. Nowadays, many investment books will offer hard and fast sell rules, such as sell when a stock meets your price target, or sell when it drops 10% from where you bought it. We're so conditioned to these rules that we take them as gospel. And they're preached widely enough that they have a significant following. I don't discard the hard rules completely; they have their purpose and can work well. But after all, didn't we put a lot of thought and research into the buy decision? Shouldn't the sell decision get at least as much thought? Click here for the video version of this story from Jennifer Openshaw.