When to close profitable position

It is a question that every trader had had in mind and it is difficult to act when the time comes. You smile when the market goes in your direction and your greed does not alllow you stop the deal. And then the market start going back and you think - it is ok, I am still winning a lot. But the market goes on in the opposite direction and your thoughts turn into 'should i stop it when I have at least something'. But you can't put up with the defeat because you was about to earn a lot a moment ago. Then, like a nightmare, the winning deal become losing deal and your fear of losing a lot makes you stop the deal. It is very common scenario. 

So, when to stop the deal? You should know the answer before jumping into position. Think of some real target level and keep the scenario above in mind. Don't regret if you could get more of the deal.