After Sam went to hell at the end of season 5, Dean returned to his old fling, Lisa, and her son, Ben, and attempted to have a regular life, bidding farewell to hunting. He even retired his beloved Impala during that time. Despite his grief and paranoia from a life of monster-hunting, Dean was relatively happy having a family.
One of Sam's most problematic decisions was trusting Ruby, even after discovering she was a demon. Unlike some other choices, Sam's decision to follow Ruby's lead was continuous, despite admitting his reservations about her. Additionally, , but instead, their volatile relationship slowly led to Sam's demon blood addiction.
To make matters worse, Sam stopped Dean from killing Ruby in season 4, episode 21. Had Dean killed her then, Sam would not have freed Lilith, necessarily, which would have prevented Lucifer from escaping hell. If the seals had been left as is, the destruction and chaos Lucifer caused once he was topside wouldn't have happened.
The article is not finished. Click on the next page to continue.