Curses aren't real. The rational part of everybody's mind knows they're not real.
But when the same thing keeps happening over and over, and no matter how many times the circumstances change a team keeps ending up in the same place, the rational part of the mind gets awfully quiet.
Really, these things only exist inside our own heads. We're only cursed if we think we are. It's a self-fulfilling prophecy. In the parlance of the shrink, our thoughts become things.