I go into most games expecting that my team is going to lose. Certainly most big games. I suspect it is a hedge against disappointment. Those of similar mind up here blame it on growing up under the shadow of the many variations of losing that the Red Sox were able to manage through 2003. Maybe so, but that was not true of rooting for the Celtics, who won a great deal in the 50s-80s. Down by 12 points three minutes left? No problem. Larry Bird will hit four 3-pointers. That Fenway malaise did not carry over to other sports.
One would think the New England Patriots, and to a lesser extend the 21st C Red Sox and the Brad Stevens Celtics would have cured me of this, but apparently not. I don't think the Patriots have that good a team this year. Of course, I didn't think so last year either, and they went to the Super Bowl. They actually were good the year before that. I can no longer remember if I was perennially worried that season or not.
One would wonder why I follow sports at all, with that attitude. I wonder myself. Perhaps it is the joy of being pleasantly surprised, or at least relieved.