Whenever your money is on the line, you will loose "cool". It is emotional.
People, hope that the price turns around instead of getting out.
People, fear that the price turns around so they get out instead of waiting their profit grows.
People are funny. Average people at least, realy funny. They hold the stocks when it is loosing value in hope it goes back, and they want to sell when it is going up in fear of loosing the profit they made.
Let's state it different: fear of making profit and hope while you are loosing?
Learn these emotions well. Fear, hope. They should not be listened to, they give wrong advice at the wrong time. It is part of human nature. When you have something like a house, you fear of loosing it. When you have nothing, you hope life turns better. Unfortunatly, it does not work in trading.
Being afraid of letting your profit grow, will limit profit. Hoping that losses go away, will stop you from action... the action of making profit instead of the loss.
The road out?
Don't trade for money - which is very emotional. But trade to trade well.