You also don't want to sell too soon or too late, which is my problem. I could have made a huge amount of cash these last two weeks if I only sold at the right time. The key is discipline.
There are also stocks you want to hold long term because they are certain to keep heading up, such as PLNI, HISC, TNOG, ITGJ, and IGTN. The thing that gets me with holding long is that you miss out on the temporary spikes, which I am now trying to take advantage of.