I gave up. According to early projections, I would have been finished by now. In terms of word count, I'm still technically on course to complete on time, even though I've not written a word for a week. I was a fast writer back in those days.
Something bad happened. Something pretty devastatingly life-changing and personal, and I took some days off from writing the novel, safe in the knowledge that I'd built myself a six-day buffer. And then, when I came back to my computer... I just couldn't do it. More than that, I just didn't want to.
It's probably because I lost momentum, I know. But it also seems a bit stupid now, writing a novel in a month. It's not going to be good, is it? You'll never be proud of the work, beyond the fact that you have done the work, and if you can't be proud of it, I'm struggling to see the point.
It's not hard to imagine that come next November, I'll be desperate to do another NaNoWriMo. But I'm hoping that that will follow a year of having tried to write a novel in normal time and failing, and not because I couldn't be bothered to do any writing in the months of the year that aren't November. (Obviously my hope is that I won't be doing NaNo at all because I'll have successfully written a novel in the forthcoming year, but... baby steps.)
This could all be justification for my quitting, of course, but really if I needed justification, I already had the Bad Thing. I think this was genuinely a good choice. I want to continue the novel (perhaps with a big rewrite of the first 25k words!), and finish it in my own time, and for it to be great. That's what I want.