There isn't a real science to this post, but I am going to write it anyway. What the heck, right? Maybe you'll agree, and maybe you won't. If anything, it will provide a little food for thought.
I recently picked up a copy of Dan Simmons's The Abominable, a book that I've been waiting for anxiously for about a year. I knew that this book was going to be a slow read, and I needed to be ready and in the right mood before I started. The book began really great and sort of tapered off a bit as I continued through the introduction. What surprised me is that the introduction was what pulled me in, and the actual meat of the narrative lost some of the magic. Allow me to explain.
The book begins with a faux introduction where Dan Simmons pulls a Stephen King and makes himself a character in the novel - a fictional version of himself and his wife. He is explaining how he "met" a man who climbed Everest, and I was enthralled by the voice of Simmons as he recounts his meetings with the man and what led to the book that I held in my hands. I know it is completely fabricated (as far as I can tell) but, it felt genuine.
I trust that version of Simmons, with his naturalistic voice leaping off the page. I wanted to read a ton more in this voice and wished that the life of the story were kept going in this manner.
Sadly, the voice shifts to that of the man who climbed Everest, and it never really recovers. It was great introduction, anyway.
My point is, we can't control this genuineness per say, but, when it flows through us - that hypnotic fever of writing that just springs forth like a stream of consciousness, it will be genuine. The reader (myself especially) can tell when the voice isn't genuine. It comes across as fake and untrustworthy, and the story that is being told can suffer greatly from this plague. I try not to force my own writing sometimes because of this. My characters know when they want me to say something on their behalf, and sometimes they don't want to say anything at all. That's okay. I will wait until they have something to say and move on to some other part of the book.
When your writing voice is your own and you've found it after a lot of trial and error, you will know. It will feel natural and your characters will come alive in it. I'm going to keep reading Abominable and see if it picks up (I imagine it will, and sometimes I really love Simmons's prose). Whatever happens in this book, I do know that I like the "real" Simmons more than I like the Simmons impersonating an Everest explorer.