I ask myself the same thing.
You may recall a few weeks ago, while on my exercycle watching the TCM series about moguls and movie stars, I was inspired by one of the names I heard. In spite of my commitment to being retired, I couldn't shake off the idea. I woke up thinking about it, played with it during the day, and tried not to think about it when I went to bed at night.
A couple of weeks after I got the idea, I made up a chapter outline.
(I'm not worried that this could be regarded as a spoiler because my handwriting is so bad not even I can read it. And I've changed some stuff. Those numbers on top are my effort to estimate the length of the book [15 pages times 13 chapters]).
But no matter how much I loved the idea (and I did and I do with an unhealthy passion), I couldn't make myself sit down and start writing. You know,Page One Chapter One. That sort of writing.
So I've been letting myself write sections of it instead, scenes I've been fixated on, hoping to get them out of my system. I figured if I enjoyed writing the scenes enough, at some point I'd write Chapter One and all that, and slot the previously written scenes in.
I may still do that. I'm writing more and more scenes. I'm even rewriting some of the material, as my mind plays around with the plot. My guess is I've written 30, maybe 35 pages. No Chapter One yet, or Two or Three. Not even the end of the book, which I know pretty much word for word.
I've never written a book this way before, so I'm not sure I really am writing this one now. Maybe I'll lose interest and never get around to the disciplined writing of Chapter One, Chapter Two. Or maybe I'll decide that much as I love the story, it is a little on the crazy side, and best left in the privacy of my own computer.
But meantime I keep writing and exploring and playing with the story. If this is what retirement will be like, I kind of enjoy it!