One of the most frequently used exercises in creative writing is the one where you "get to know" your characters. You fill a notebook or fifteen pages or some other hideous number with important and more often unimportant information about the human being you're creating: you write about when the character's birthday is, what kind of parties he likes to have, what's in his pockets, what he wears to bed, what's on his bedroom floor, who's in his family, who he doesn't talk to anymore, what sort of relationships he's had in the past, what sort of lover he is, his favorite movies, his favorite music, his favorite books, his shoe size, what socks he's wearing (do they match?), what he does for a living, his hobbies, his obsessions, his fears, what he dreamed about on Tuesday, his relationship with his father, his favorite food, his least favorite food, his allergies, how he did in school, did he go to college, does he have a good job, and so on, and so on, until finally you know this person completely.
This is one of those things that makes intuitive sense but doesn't, I think, hold up to practice. There are two reasons for this: one simple, one more complex.
The simple one first: What kind of socks your character is wearing becomes irrelevant the second a good story begins. Why? Because you're telling us about the most interesting moment in that character's life. Something that changed him or her. And if he's still thinking about his damn socks, you've failed; you have not found a sufficiently interesting event for this story. There are probably two or three things about your character that matter after The Event, and you very likely knew all of them before this exercise, because they were important. Even if it was socks, they were important socks -- or at least, the socks were very important to him. So important that their absence could shake his world to the core. That would be interesting -- if The Event began with socks. But if you're not shaking your character's world to the core, you're very likely doing it wrong. Which means that whole notebook you just filled will immediately become irrelevant.
Secondly, your character isn't wearing socks. Not until you say he is. The character as an object of knowledge, in fact any fictional entity as an object of knowledge, is a really interesting creature, because it exists in reference to your fiction's needs, and in reference to what's pertinent. Many writers believe that their characters existed before they found them and will continue to exist thereafter. I find this unlikely. Even if it's your experience as a writer, it's not the fact of the text: the fact of the text is that he isn't wearing socks until they become relevant, or if he is, we have no idea what kind until you tell us. Imagining that your character extends very far beyond the text seems a source of much trouble in fiction. You want the reader to infer, of course, and we will generally infer socks if the character is shod -- but if you don't stay very clear on what is about the character and what merely might be inferred, you are likely to write very dull fiction. I have seen instructors say that a draft is incomplete because the writer doesn't know the character well enough, and I always feel that this is severely unlikely -- that because the character will always and only emerge from the action and event of the story, the real trouble is that the action is insufficiently clear or interesting.
Think about the difference in reality between a character described through knowledge that existed before the character was written in this scene and described through knowledge of action in the scene. The latter always feels more persuasive, more real: it feels as if it is actually happening, or happened, even if it's impossible. I never believe any "background info" for any character. It seems false, because it seems to preexist the text -- to be something forced on the text by the writer. I think a lot of people feel this way. Maybe most of us, now.
The exercise is most often used with beginning writers, which is ironic because I always feel as if beginners tend to know too much about their characters. They know how they look, how they feel about each other, what they did yesterday and the day before, what they will do tomorrow. They fail to discover the character through writing, where we can see it. Their knowledge allows them to forget to use the text and the page -- so often, the action has already happened, while I wasn't looking. The characters have been defined elsewhere, outside the text. And so I can't know them here, and now, within it.
To tell you the truth, I often know next to nothing about my characters. I don't know much about how most of them look -- rather, I imagine their appearances as the intersections of many probabilities and possibilities. I know parts of their bodies much better than others. I know parts of their backgrounds very clearly but mostly not at all. Frequently I forget their names mid-draft. This is partly because I am forgetful. I am an extreme case. But it is partly because I believe that plot and action and story are what happen when I engage, now, with a text. When I am writing I discover my characters, my false people. This sometimes lends them a sort of flatness, I'm sure. But our knowledge of each other is also flat. Our knowledge of ourselves is flat. Our knowledge of every character is flat. Complexity in fiction is usually one of two things: legitimate mystery, or shallow artifice. When it comes to character especially, it is shallow artifice. I find it irritating, honestly. I do not believe in complexity. I do not believe in fiction as a site for knowledge. It is a place where we do not, should not, know.