Good things happen to both optimists and pessimists, but they view those victories in very different ways. An optimist will celebrate what has happened and view themselves as the reason for the victory. This will usually propel them towards more victories. A pessimist will be surprised at their victory, believing they had nothing to do with it and it was completely a fluke, and they will worry about what is going to go wrong now to balance out the good that they are experiencing. This will usually propel them to a failure in the near future.
For instance, an optimistic person who receives a raise will recognize that their hard work paid off and enjoy the fact that they have gotten the recognition they deserve. A pessimistic person will not understand why they got the raise and worry about there being an ulterior motive behind it, such as more work and responsibility. That worry will cause them to become paranoid and less effective at their job.