And I find this fascinating, as I'm just the opposite. My characters don't exist outside the novel. What do they do when the authorial camera isn't on them? How the fuck should I know? Ask me what music the main character of my novel (the one I'm trying to sell) prefers, or what she likes to eat, and I'm like, dude, relevance? Of course, I am 98% a short story writer, and it's more usual there to see characters as mere one-off beings led around by the plot/idea. But as I've said, I think this even about my novel characters, who I should theoretically feel differently about. I know my characters inside and out as it relates to the story, but once they're out of it, they collapse into nothingness. (I've also never been tempted to write fanfiction, for similar reasons; to me the characters only exist inside their "world." I'd be more into writing shared-world fiction, using other people's ideas, but haven't ever done that either.)
I've always been this way, from the time I first started writing. School writing exercises killed me, because so many of them were along the lines of "fill out this survey about your character." As someone who didn't even like filling out Internet surveys (do the kids still do those?), filling it out about something that to me is essentially a plot element was difficult beyond all comprehension. I've never cried when killing a character. I've never felt a flutter when making them fall in love. Even more so, I've never, ever had the sensation of my characters leading my plot in new, interesting directions. I almost wish they would, because that would take some work off of me! But really, I always know where my plot is going, and once I start constructing my plot (and my plot is always fully constructed before I write a word), the characters fall into place like the cogs and sprockets they are.
I don't consider this "writing method" to be a plus, by the way, or say it's the way all writers should act toward their characters. In fact, it probably causes me to be way less prolific than I would otherwise be, if I were the kind of person who could throw caution to the wind and crank out thousands of words of character sketches or bonus materials. It's the difference between a portrait painter and an action painter; yeah, the latter creates a lot of crap, but in the end, they probably create just as much usable material as the one who doesn't waste a single stroke. And they have a lot more fun doing it! But I am who I am.
Now, reading this you might think that I write something along the lines of military SF or other plot-centric genre, where Spock-like characterizations rule. However, this is not so! Those who have read the novel I'm trying to sell have called it out as extremely character-focused, which means I'm probably pretty good at hiding the fact that I don't care about my characters. Or, more likely, that science fiction has pretty low standards for a character's "roundness."
So, writers that read this blog: which way do you go? I really think that I'm in the minority on this one, and I'm a little envious of those who can do it the other way. But I also think it would be hilarious if someday the novel is published, and people started writing fanfic based on it, and caring a lot more about my characters than I ever did. Don't you know, that lady's only a plot element?