I wanted to give you a weekly gem from G. C. Selden (Psychology of the Stock Market).
"To a great extent, we train our judgment to lend itself to our selfish interests. . . To make the greatest success it is necessary for the trader to forget entirely his own position in the market, his profits or losses, the relation of the present prices to the point where he bought or sold, and to fix his thoughts upon the position of the market. If the market is going down the trader must sell, no matter whether he has a profit or a loss, whether he bought a year ago or two minutes ago." (p. 57)