As an author, it’s important to see the characters you create as real people. That may sound like a contradiction, but it’s true: if you don’t consider your characters as humans with feelings and thoughts and motivations, your readers won’t either. I don’t think this is a controversial opinion, but I also don’t think anyone with a normally functioning brain can pull it off. To write multiple people, you have to be multiple people. Forget the duality of man; embrace the infinity of identity.