The fact that I don't expect a very good outcome doesn't mean I shouldn't try, because what the hell else can I do? At worst, I get useful information out of my (likely) failures.
Also, thinking and preparing for the worst doesn't need to be a gloomy thing. It can even be empowering. When I've thought of all the possible crappy outcomes that might happen, I can be confident that whatever happens, I'll survive. I wish more people were like me; I'm confident that lots of disasters in the world could be avoided if people just took their heads out from the sand and embraced all the horrible possibilities that exist.