Percentage should not determine why we should sell or hold. Remember that those that are patient will make good profits in this market. Trading is a game and you need to plan and know how long you can hold before investing your hard earned money.
Planning! That is the best word for it. A lot of people that want to take advantage of the market fluctuation enter it the same way of gambling, and if you do that, you are simply exposing yourself to a huge risk as a trader. Without a trading plan and strategy, it is just plain simple, you are gambling and the outcome is always horrific. Making profit in the market is one thing that has to do with your level of anticipation, knowing what to look out for before you anticipate, and having in mind where you want to be stopping loss based on your reward to risk ratio. All those put together coupled with other few things, makes up a plan.