I am noticing a lot of parallels between season 4 and season 10. In terms of addiction; Sam was slowly sucked into demon blood addiction in season 4 while Dean was slowly sucked into addiction to violence in season 10. Dean was operating at a deficit in season 4 while Sam was on deficit in season 10. When they had that siren fight; Sam said Dean was holding him back; When they were trying to help Jimmy Novak’s daughter, Dean implied that it was Sam holding him back. They were both led astray by demons; Sam by Ruby, Dean by Crowley. They had these monumentally huge fights at the end; Sam won in season 4, Dean won in season 10. At the end of the day though…they still end up together…and they’ve fucked up the world.