William DeWitt Hyde quotes:

Unsatisfied desire is the characteristic feature of human life. That is the common fact out of which both pessimism and optimism are constructed. Dwell on the impossibility of ever getting a state of complete and permanent satisfaction with what you have, and you become a pessimist. Dwell on the opportunity for endless growth and conquest which this same fact makes possible, and you become an optimist.

An opportunity is a conjunction of circumstances by which one may improve his condition of life or his equipment for life.

Live in the active voice, rather than passive. Think more about what you happen than what is happening to you.

Live in the present tense, facing the duty at hand without regret for the past or worry over the future.

The world we live in is a world of mingled good and evil. Whether it is chiefly good or chiefly bad depends on how we take it. To look at the world in such a way as to emphasize the evil is the art of pessimism. To look at it in such a way as to bring out the good, and throw the evil into the background, is the art of optimism. The facts are the same in either case. It is simply a question of perspective and emphasis.