One of the oddest pleasures of NaNoWriMo is that you have no life during November. This sounds weird; why is it so much fun to spend practically every spare moment working like crazy on a book that will almost certainly never be published, and only rarely seen by anyone else?
The death of your social life means that you end up very focused for one month. It's astounding what you can accomplish when you really put your mind to it. You end up discovering that inspiration is not really all that great as a motivator, and it usually only comes after you've been truding through dialogue and plot points for an hour. When you write yourself into a corner, you will discover wells of creativity in yourself that you never dreamed were there!
It also means that for a month, you get to try on the persona of a writer. Instead of being an accountant or a sales clerk or a student, you get to be a creative individual, producing a work of art from your own head! For one month, you are an artist, a creator in touch with the muse! But at the end of the month, you get to resume your normal life. You get the best of both worlds!
But the strange thing is, your normal life is never quite the same again. You overhear conversations, and think "That would make a great scene." You sit watching sunset when you're stuck in traffic, and start trying to describe it. Little plots and scenes crop up in your consciousness from time to time. You keep hitting the word count button, even on office memos.
NaNo: it's not just a month of insanity, it's a way of life.
(C'mon, November! Hurry up and get here!)