I believe that every sports fan, to really mature as a fan and come to understand what's so great about rooting for a team, needs to go through a few years of really mediocre or awful teams. A lot of college football fans scoff at the smaller bowls, for instance, but after you go to every home game of an 0-12 team, you really gain a sense of perspective.
I can't really respect fans of teams that don't have the experience of watching a really bad team. I guess it's not really the fault of Yankees fans or any of those other perennially good teams that they don't have a concept of failure, but I still can't respect them. Even if it's a tradition long passed down through a family that does remember when the Yankees suck. But it's worst when it's someone who just wants to cling to a successful team. Those guys don't get it at all.