Many traders take a profit at their profit target. Then when they see they could have made a greater profit, curse themselves. That is a terrible way to live. With a negative outlook, even if you are a winner, you make yourself a loser.
Michael Gur, CTA

On the other hand many traders get excited and trigger happy, thinking of the fast and quick $ on offer. Overoptimism sets you up for disappointment and loss of confidence eventually.