There are two kinds of sculptures. There's the kind that subtracts: Michelangelo starts with a block of marble and chips away. And then there is the kind that adds, building with clay, piling it on. The way I write novels is to keep piling on and piling on and piling on.
One has to be able to twist and change and distort characters, play with them like clay, so everything fits together. Real people don't permit you to do that.