There is an old rule in the market, often repeated by Jim Cramer on his "Mad Money" program on CNBC: "Bears win, bulls win, pigs get slaughtered." This means that those who hold on to their stock to long end up losing money.

So, when you should sell your stock? Sell strategies are just as important as your buy strategy. It seems everyone has their preferred way to buy. Every investment newsletter lists stocks to buy now; your broker has her favorite "strong buy" list; your friend at work has his "can't miss" stock to buy now; heck, even the taxi driver has their favorite stock idea. Let's assume they are each right with their picks. You followed their recommendations and the stock has gone up. What do you do now? Do you keep holding, hoping it will continue to go up? Do you sell it all, or maybe sell some of it?

Well, these are all good questions, since you do not make any money until you sell what you bought. To bad none of these people told you when to sell. Up until now any gains you have are unrealized and exist on paper. Only when you sell do you actually realize any profits from your investments and trades. Now, if you only knew what to sell and when to sell it. Actually, there are five reasons to sell stocks that have unrealized gains:

The price has reached the predetermined target you established when doing your homework before you made your purchase;

The price drops back down to your trailing stop order that you have set according to your stop rules;

You need the money for some other purpose (to buy another more promising stock, to invest in some other asset or for some other good reason;

As a part of good capital management you wish to realize some of the gains and reduce your holdings of this stock; and

You have reached the end of the time you gave for this stock to perform and you believe there are better opportunities.

Today, let