I am surprised nobody mentioned ownership. Teams will be sustainable with owners like Kraft and Rooney. I don't think they ever could be with owners like Mike Brown and Daniel Snyder.
I think you need a GM and coaching staff, along with a few other key players, that engender confidence and trust. How can the Patriot players not believe in BB's ability to game plan and out-scheme other teams. Think how many times we saw Marino, down by 3-4 points with 2-3 minutes left in the game, and come away with the win. Heck I almost preferred to be in that position as I had so much trust in his ability to come through. If I felt that way how, could his team not feel the same?
In any venture, if you feel ownership is clueless and leaders/managers are mostly concerned with their own agendas and egos, well you know you are part of a cluster **** and start being more concerned about yourself than the team. That is the antithesis of sustainability for success IMHO.
Sure, I could say thinks like, "it all starts with running the ball and being able to stop the run" or "you must have a franchise QB". Truth is I feel those things only matter IF you have leadership from the top down that has a vision, structure, and game plan that you can believe in as a recipe for success.