Optimism is "an inclination to put the most favorable construction upon actions and events or to anticipate the best possible outcome".^[1] It is the philosophical opposite of pessimism. Optimists generally believe that people and events are inherently good, so that most situations work out in the end for the best.

Alternatively, some optimists believe that regardless of the external world or situation, one should choose to feel good about it and make the most of it. This kind of optimism doesn't say anything about the quality of the external world; it's an internal optimism about one's own feelings.

A common conundrum illustrates optimism-versus-pessimism with the question, does one regard a given glass of water, filled to half its capacity, as half full or as half empty? Conventional wisdom expects optimists to reply, "Half full," and pessimists to respond, "Half empty" (assuming that "full" is considered good, and "empty", bad).

Another paradox sometimes associated with optimism is that the only thing an optimist cannot view as positive is a pessimist. Pessimism, however, as it acts as a check to recklessness, may even then be viewed in a positive light.

http://en.wikipedia.org/wiki/Positive_psychology

http://www.brainyquote.com/quotes/keywords/optimism.html

http://www.newsweek.com/id/61572      This is your brain on optimism