Optimism is a philosophy and a way of life. Optimists believe that the world is generally a positive place to be in. In the view of an optimist, people and things are good. Many liberal optimists do not believe in original sin.
Optimism basically looks on the positive side, believing things will work out in the end. When a person is optimistic, it doesn't mean that they never doubt themselves. They might have a bad day or two. They recognize that they can make things better; there is a lesson to be learned from this, and they will move on.
Optimism is associated with the idea of a glass looking "half full", instead of looking "Half empty".