One of the interesting things about coming into a fandom long after it has been established is discovering common themes in the fanfic. In a lot of cases, if you just read the fic, and never saw the show, you'd come aways with a totally different idea of the characters from things that keep popping up over and over again. What brought this to mind specifically is coming across yet another fic where Ezra considers Josiah some sort of father figure. That's one of those common themes in M7 fic I keep stumbling over, but as far as the show itself goes, I see nothing to indicate just where that comes from.
So what are some of the fanon canon things in your favourite fandoms that baffle you?