Success.
If losing could do it, we would have been there and remained there long ago. It's been our common denominator.

They need to share a common vision that binds them in purpose. I believe it is beyond terms like "culture" and "scheme" and such. And its proof of validated legitimacy will be evidenced and measured in individuals. That is after the fact necessarily. A "team" chooses to succeed, and to be such. "Winning" is a yardstick that is long: One season long; one game long; one series long; one play long; a yard. That makes it frail, and it makes it vulnerable. How many ways have we seen it destroyed and denied? A team is never an accident though it may come as a surprise. Nobody regrets winning a Super Bowl.