According to Dr. Martin Seligman, former president of the American Psychological Association, there are several differences between optimists and pessimists.
Pessimists explain negative events as a permanent fixture of their identity (something they can’t change). They view themselves (or life in general) as the problem, and there is nothing that can really be done.
Optimists explain negative events as situation and short-lived. When something goes wrong, they focus on situational factors that can be altered and improved.