"Pozitively Pozitive"

Does anyone truly believe the claim that thinking positively leads to pleasant events, while negative thoughts induce unpleasant occurrences? Or is it just another adage that encourages us to believe that we have control over what may, in fact, be utterly random? Yes, I suppose I am becoming far too cynical, though I can't deny the fact that assuming the worst is exhausting. Optimism would, in fact, be a relief. But then again, I fear that if I persuade myself to not assume the worst, I will be: deluding myself/not preparing myself adequately/basically, not girding my loins, and other such irrational fears. A middle path must be sought.

Whoever thought that even optimism could be an ordeal?