This is a very classic mistake. Young traders are too quick to take a small profit when a position starts to go their way and miss the really big move. Be patient with winning trades.
Apple is a great example. If you had made a $10,000 investment in Apple in July 2002, nine months after the release of the first iPod, you would be a millionaire today.
However, how many people do you know who became millionaires trading Apple? Apple is an example of a company that everyone knows about; its explosion was in front of everyone's eyes; but it remained under owned by the public.
Read MoreHey, summer interns! Get THIS right. Seriously.
You may have heard ridiculous phrases like, "It's had such a big move, it can't go up anymore." In fact, when the stock was trading around $700 (before splitting 10 for 1), I heard more Apple bears than bulls.
Perhaps, it's human nature to take small gains. However, to really make a lot of money trading, you should try to be very profitable on a few trades, as opposed to trying to be slightly profitable on every call. After all, at the end of the day, there is only one way to keep score.