There are loads of different ways in which people write stories. Some plan to the nth degree; some travel the world to obtain inspiration and pad out their work with research; and, some allow their characters to create the story.
Sounds far-fetched doesn't it? When I first came across this it was one of my independent author friends, Caleb Pirtle III, that mentioned the phenomenon. At first I believed that it was another indie idea that was outside the usual publishing and writing box. However, it didn't take me long to find that some globally recognised authors write in similar ways. The first one who displayed similarities was Ian Rankin, creator of the Rebus novels.
One of the benefits I have found in writing this way is that you are not constrained by a plan, which can happen. I have written this way since beginning eight years ago. Most recently Philip Pullman creator of the Dark Materials trilogy and now The Book of Dust. In advice given to budding authors he says 'let the characters lead you through the story'.
Of course, it isn't as straight forward as it sounds, you need to be confident in your characters. For me, I had created the character, Patrick Steele, in my mind before ever putting the proverbial pen on the page. It is rather like a child creating an invisible friend. Such creations are 'real' in the mind of the child. They have conversations, go to different places and tell secrets. What else is a character you create in a book?
Then it takes a degree of courageousness to allow the character to take the lead. The tendency is to believe that the story is yours, which of course is true in one way, but in that attitude lies painful days filled with writer's block. The characters you create suffer no such limitations and will lead you through the events and relationships that you began.
To a degree there is an amount of magic in the process. It pervades all creativity. When you consider that writing books begins with nothing but words that then are moulded. combined and ordered into something entirely new and unique. In that case it is hardly surprising that the characters within our stories are the ones in control. After all, we give them their characteristics and should feel comfortable in their ability to handle the task.