Dean is not possessed by anything. It’s his own soul that’s been twisted into a demon soul, so this demon is not anyone other than Dean. So every thought, every action, that’s Dean, as opposed to some other demon possessing him. So while he’s a demon, that causes some complication of thought in him in that, “This is really me doing it.” It also motivates a certain bravado. “Yeah, this is me doing and owning it!” There’s a real period for Dean of deciding how dark he’s going to be and what kind of demon he’s going to be, because he can’t blame it on anyone else but himself. And then afterwards is when it will have the most effect on him because it was him. It was his actions that led him to becoming a demon. He pushed it with the Mark. He pushed Sammy away at the end of last season. He said, “I can do this by myself.” So there’s a certain consequence to all this that is almost more interesting to us than the actual demon part.
Jeremy Carver on Demon!Dean in Season 10[x] (via casfucker)