Writing is an art, not a science, not maths. It’s not a simple case of a + b = c.
If you’re writing a biography or someone’s memoirs, you take all the stories they tell you, all the cold hard facts at your disposal, and put them together in a cohesive manner. But it’s more than that. You learn as much by the things they don’t tell you as by the things they do. You learn by watching them interact with each other and with you. Those intangibles have to make it into the book as well, if you want to truly represent their lives.
If you’re writing a novel, you have to know your characters backwards and forwards, inside and out. You know what they eat when the sneak into the kitchen at 2 a.m. for sustenance. You know which musician is their favourite. You know their favourite book, their favourite movie, how they dress, what they said when they sassed their parents two weeks ago. Sometimes the characters wreak havoc on your carefully detailed outlines. You may think that you’re writing this story, but then a character turns into something much more than you would have imagined, and tells you that the story actually goes in a different direction. If you’re a good writer, you’ll see where that takes you. If it takes you to a good place, then run with it. If it takes you to a bad place, perhaps that character isn’t one you need in your story.
Never think that the characters you’re creating aren’t real. Izzy and I wrote a book some years ago, and we had the experience of someone we’d planned as a minor character developing a very strong personality and completely changing the way the book unfolded. We still got to the ending that we wanted, but took a different route to get there. This formerly minor character is actually living the life one of our real life friends is living now. As we had dinner with this friend a few weeks ago and she was telling us about everything she was doing, all I could think was, “Wow! That’s what Celia did!”
Writing can take over your life if you let it. Sometimes that’s a good thing; sometimes it’s a bad thing. But mostly, I think, it’s a good thing.