What Happens When You Expect the Worst?

When good things happen to people who overthink in this way, they still tend to have an impending sense of doom. It's a self-fulfilling prophecy. If you expect the worst, you might create the worst because how could there possibly be any other situation? And I think people who have this thinking style would rather be in charge of a bad situation happening than have it catch them off guard. So what do we need to do to make sure we don't always expect the worst in every situation?