Howling:"X is really Y" theories: why?

I'm curious why there are so many fan theories that established character X is really earlier established character Y in disguise.

If the answer were just, "Because they've done it before," that would be that. But I can't think of any examples. Sure, often a newly-introduced character turns out to be the Master or Rassilon or whatever in that same story, but have they ever followed someone as a recurring character over multiple stories and then revealed him to be someone else? (Yeah, I know about Harold Saxon--but we didn't actually see him at all until Utopia, much less see him as a major character; he was a background plot detail that we kept hearing about.) But maybe I'm missing something obvious.

So, what _is_ the explanation? Why do people always think that the Rani, Romana, Susan, Jenny, the Monk, etc. will be introduced disguised as another major recurring character, when that's never happened before?

(I'm guessing Delton Menace's answer is going to be "because people are stupid", but I'm hoping for something that gives a little more insight. Why? Well, we know that SM, like RTD before him, has heard all these theories, and even jokes about them. I suspect he's also tried to figure out why. And he likes to play with people's expectations.) --Falcotron 05:55, May 6, 2010 (UTC)


 * You're trying to puzzle out why fans come up with theories for things? (Visit the various Doctor Who forums like Gallifrey Base Forums and Doctor Who Online for plenty of discussion).
 * You're mostly right when you say 'because they'd done that before', but you rather than just in Doctor Who it's something about the wider media that we're exposed to.
 * We expect things like this to happen, in modern drama and science fiction drama we're used to story arcs and hidden revelations. Series like Lost, Battlestar Galactica (the reboot), Babylon 5, Spooks they're all series' that have long story arcs, with individual stories that make up the larger whole and that have had character revelations or other sorts of things that are revealed throughout the course of the series. --Tangerineduel 06:19, May 6, 2010 (UTC)


 * Yeah, I've read those forums; that's where I see most of these fan theories. And I see people calling them stupid. What I don't see is anyone asking this question seriously, or getting a serious answer.


 * And the reason I'm trying to puzzle it out is, as I said, I suspect Moffat has tried to puzzle it out, and has probably succeeded better than me, and that might even influence his writing....


 * Anyway, that's a great point about other SF series. Some of them have had the big reveal be "X and Y are the same person" or "X is an alternate version of Y from another timeline" or whatever. Thanks. --Falcotron 06:29, May 6, 2010 (UTC)