Optimists tend to interpret their troubles as transient, controllable, and specific to one situation. Pessimists, on the other hand, believe that their troubles last forever, undermine everything they do, and are uncontrollable.
The only thing that scares me more than space aliens is the idea that there aren't any space aliens. We can't be the best that creation has to offer. I pray we're not all there is. If so, we're in big trouble.