Three things. 1. Building farm system, and relying on it too fast 2. Constantly changing GMs with the new ones inheriting the problems that the other one got fired for 3. Just not making smart moves, ie having multiple players for one position, or Bregman/Devers fiasco.
Beyond that, Im a believer in the old school ways, especially for this team at this time. I think these new analytics guys got the players thinking too much, and not playing enough. Bad coaches and manager, except Varitek and maybe Assistant Manager.