OK, so, I've knocked on NaNoWriMo before. I honestly think it's a good exercise, a way to learn your writing habits, figure out how to write a novel, and understand the way you work.
I don't think it's a good way to get great work.
This, of course, took first-hand learning.
The three years after the failed project fell apart involved several false starts for novels, most of which were connected to the worldbuilding work I had done in the fantasy setting. I had done tons of detail work and history work-- work that still stands, as it is the world that Thorn and Mages is set in. And I think a big part of the challenge I had to get over was understanding that just because I had done all that worldbuilding work, it didn't mean I had to share it all.
What I had kind of settled on was the idea of writing a series that was the proto-Crown of Druthal, though it was set in an embassy instead of a ship. But the "Explain All The Things" part of my brain felt I had to properly set things up. That readers would need to know the WHOLE STORY to make sense of things.
I think this is a trap fantasy writers often fall into.
Anyhow, this became the central idea behind what I would make my 2003 NaNoWriMo project: The Fifty Year War. A novel which would flesh out the history of the war between Druthal and Poasia. You know, the stuff that readers would be dying to know.
Now, I did succeed as a NaNoWriMo, writing around 53,000 words in November. And the "finished" first draft was around 60K.
But it was horrible.
It was a novel in which I had clearly absorbed all the wrong lessons from Isaac Asimov and David Weber. It was a novel by the way of interconnected novellas, like Foundation, but unlike Foundation, there was no central theme or core to carry it through. And certainly no core characters. The closest thing to a central character wasn't a character, but a series of descendents in the same family who serve in the war. It was a novel in which, like Weber's Honor Harrington books there are several meetings, in which people you never met before and won't meet again tell each other things that you don't care about.
Fifty Year War was a book with no heart, no soul, and certainly nothing resembling a proper plot. It comes across as a bad prequel to a thing that didn't exist yet, hitting the notes to set things up in a perfunctory way, without any sense that those set-ups existed for any organic reason beyond "set things where they needed to be".
IF I HAD SELF-PUBLISHED AT THIS POINT: At the time I really believed in Fifty Year War, though for the life of me I don't know why I thought that. It isn't an interesting work, but if the means had been a bit more convenient at the time, I might have convinced myself it should be self-published. And I would have been wrong, because it is awful. Further revisions made it less awful, but it is such a mess at its core, no amount of editing could save the patient. So, if I had put it out there, it would have failed, and it would have felt like a toxic albatross on my name and the world I had built.
BUT DID I LEARN ANYTHING BY NOW?: At this point, the main thing I had learned was-- roughly-- the discipline behind writing a novel, the level of planning that needed to go into getting it done. But even then, I was still untempered. I needed to figure out what a novel was beyond "a whole lot of writing". But reaching the point of sitting down and writing a novel-like-object to completion was something of a milestone.