It's the 5th day of NANO and to stay on point with the goal, by the end of today the 8335 word mark needs to be reached.
If the entire novel will be 50,000 words, you're at the 16.6% mark. Of course, if the finished book will have far more words when completed (like 90,000, 100,000 or more) this percent point to the true end will be smaller. We're talking today about being at least 15% of the way into the story though.
This is where some of the things are out of the way, the major characters have been introduced and the goal or quest has been presented and the first steps toward that goal might already have been taken. If they haven't been, it's time to do so now. And just as important, something major has happened.
15% of the way into a story is the equivalent of the first three chapters in shorter tales. In page count if you're getting 290 words to a page (which what I was averaging when last checked) you'll have 29 pages at the end of today. For some that equates to two chapters, to others it will be three. For those who specialize in lots of short chapters, it will be more. However you've set things up the only thing that it shouldn't be a single chapter. That's simply too long. In the long run, readers want a chapter that they can read and move on to other things.
We want them to stay in their seat turning pages. But frequently that's something to ensure in the editing and polishing stage and with NANO it's pounding out that first draft that is the project.
So, at 15% of the way in it is time for things to change. Cast is on the stage; the destination they need to reach has been given. The destination could be to find a killer, win the girl or guy, return The Ring to the volcano and destroy it, best the enemy, discover the secret or the treasure.
It's time to move the cast forward and to do so, the next stage in the "operation" is entered.