It doesn't matter if the story you've been carrying around is fiction, memoir, non-fiction or some creative blend, there is a reason you need to tell it. And once you know your 'Why,' that little voice that's been stopping you from writing won't stand a chance anymore!
And something I didn't mention in the video but should have, which may not make sense until you watch the video/read the transcript:
If more than one of your answers is out of your control ("My contract requires it") or because of another person ("My husband thinks it's a great idea"), do the exercise again until all of the answers you hear are personal and within your control.
If you can't get to that place, of having a personal reason why this book is so important to you, maybe consider that the book you've focused on might not be the one you should be writing, right now... just consider it.
That may be why you've been struggling to start or finish it.