Sam Winchester: I think it’s a temporal paradox. We pulled Dad here from 2003, right? So time is self-correcting. Our timeline is changing to this new one.

Dean Winchester: So, what do you mean?

Sam Winchester: It means, I think, that, if we don’t fix this, then we become those other versions of ourselves. Like, for real.

Dean Winchester: Okay, well, I’m cool, but you’re… ugh.

From Supernatural – Season 14 Episode 13: ‘Lebanon’ (14×13)