I'm highly sleepy, so let's all hope that this makes sense in the end. It seems like everyone in the HP fan world has some ship they like (ship = pairing, for those not in the know. Harry/Draco, Dobby/Padfoot, etc). Oddly, the number of pairings I *don't* like greatly outnumbers the pairings I do... but only on the surface it seems.
Draco/Hermione is a typical example. I say to myself (or my computer, cat, whatever) that I don't like that pairing. It makes no sense. The characters would never end up as friends, let alone in bed together... but then I find a story where it works. Tonight I gave up on TV and read Christmas Is In the Air... Don't Breathe Too Deeply!, a rather funny short story about Draco and Hermione hitting it off over Christmas break (and Lucius Malfoy and Dobby on holiday together, heehee). When I finished reading it, I had no qualms with those two having a physical relationship.
Snape/Harry is another one where I just put my foot down and said 'No no no! Just no way! They cannot be friends!', but then I read Clipped Wings (I can't find the URL, I think it's on isiscolo's recs page), and once more I had to change how I felt about it.
So see, there are so many times when pairings shouldn't work, but a story makes it totally believable. I wonder if that says something about me? Am I too closed-minded? Do I think I know the canon so well that I'm not open to possibilities? Or am I totally backwards on this and somehow writers are skilled enough that they take the character, keep it to be totally on-character, and yet still somehow make the situations believable? I guess there's a third option, too: How much does the situation play a part in this? Could the setup be the key?
That story I mentioned earlier today, the one about Goyle/Colin, it had only the most barebones situation enabling the slash part of the story (the two were at the lake together and Colin checked out Goyle's body). So in its case, the pairing-which-shouldn't-work didn't get (much) help from the setting/setup. The writing was good, but not the most amazing I ever read. So why did I finish the story buying that the two of them really could (in the books) somehow end up having sex together?
I wonder if it's sort of like on a MUSH (online RPG): You apply for a character, you RP it, and if you're doing it right then your character will grow and change. Character development. But if a MUSH character grows and changes, it's usually in a... "linear" sort of way. In general, characters don't just turn gay overnight (snerk snerk to the one person who might be reading this and is the exception to that rule). So why does it work in fanfics?