Not selling a winning stock too early is a big psychological task for a lot of traders. As soon as the numbers are green,you begin to feel tempted to protect your gains and sell parts or even your entire position.That is just because of fear.You should not sell your stock, unless it gives you a clear warning signal.Most of the time that is selling on increasing volume,while also failing to make higher highs. But those warning signals can differ from stock to stock. It also depends on how strong the correlation between the stock and the broader market is and how strong the sector of the stock is performing. Also news events can change the behaviour of a stock temporarily.
All of those points have to be considered,before entering a position,so that you are prepared for everything that could happen. But never sell only because of a strange gut feeling. You have to ask yourself,why do i want to sell now.If the answer is not rational,don’t sell. If you don’t hold on to your winners,you will never make money consistently in the markets,because there will always be losers. If you want to scale out of a position you have to set targets for your exits,and if the price doesn’t get there,you will get stopped out with a small loss,so what?Still better than missing every big move in stocks that you sold too early just because of fear.