It is simple - you earn or loose money only when you sell.
The price can go up or down, but you are richer or poorer only when you sell your actives. So keep it till you earn what you wanted.
Until then, say good buy to your money and sleep well.
The second rule coming from the first, is to invest only such amount that you are ready to forget about. (Never on the only money you have and never on other people's money.)
