For the writer, I think the expectation of a bad outcome is something of a self-fulfilling prophecy. It is, at least, if we allow the expectation of a bad outcome to keep us from working and from circulating our work.
Writing is meant to be shared. If we are unwilling to share our written work (or if we produce no written work), then we fail as writers more surely than we could possibly fail by handing in a poor draft. At least when the deadline comes, if you have turned in nothing, you have no chance of your work being accepted; if you have something written, you have a chance--however slim you may believe that chance to be.
If you believe the outcome will be bad, you almost guarantee the bad outcome. This is often true in interpersonal dynamics--whether interviewing, presenting work, or even dating--if you show a lack of confidence, the audience will expect problems; if you show confidence, you're often well received.
It is true to some extent in presenting written work: often people present the work along with a long list of the problems they still see, with no comment on the good things they have accomplished--they're so sure the reader will see the problems that they want the reader to know that they've seen the problem, too. But this can backfire, especially if you see problems that your reader wouldn't have.
The old adage "you can't win if you don't play", is kind of true and kind of annoyingly simplistic. But the outcome of not playing is often exactly like the outcome of losing, except perhaps in the expenditure of energy. But that's not really a loss, is it? What good is it to be well rested, but still have the dissertation waiting to be written?
I suppose there is the fear that if one does try, one might be ridiculed for one's efforts, whereas the person who shows nothing, is not ridiculed. Of course, if you fear ridicule, you might also fear the ridicule of never finishing. Is it really worse to be known as the person who went for it and failed than it is to be known as the person who never went for it?
Chance always plays a role; it's always possible that one will find a winning lottery ticket on the street. But barring random chance, I feel like pessimism is a self-fulfilling prophecy.
Getting things to work out right may be more difficult, but I believe that the optimistic mind also creates a self-fulfilling prophecy. Confidence helps one perform better. Optimism and confidence also make the moment more enjoyable. If you can maintain optimism during a project, even if it doesn't work out, the act of working on the project may not seem so onerous, because it is an act filled with hope.
For my part, I have to work to keep an optimistic mindset, and it often slips away. Nonetheless, I believe that work in trying to be optimistic and in practicing believing in myself, is worth the effort.