I've always assumed that it's better to have low expectations for things that you have no control over. That way when you find out what the result is you will be less disappointed if its bad and happier if its good.
But what if you have to wait a long time for the result? Life is short. Every day you wake up with about 16 hours to run around and do stuff before the glycogen stores in your brain start running low and the adenosine receptors signal that it's time to sleep and recharge again. How you feel during those hours definitely matters. In fact, lots of people think that being happy is the most important part of life!
I think that the best strategy given these goals is to try to feel lukewarm-good about your result while waiting. But refuse to commit to any specific predictions to yourself or anyone else. Then, right before you are about to get your result, force yourself into full worst-case scenario low-balling mode. If you can pull this off, you get the benefits of being aloofly happy about your result most of the time along with the benefits of low expectations to mitigate post-result depression.
