Generally speaking when I write a first draft I end up writing about a third of the book all at once, and then end up tired out and lag for months before knocking the rest of it out. Needless to say, I've got a stack of unfinished novels. I've finally passed my marker with The Hellfire Legacy, and am fairly confident about wrapping it up.
Of course, I have a list of other things to do as well. I beta read for folks, and have a couple such on my plate at the moment. Have to edit another novel. Finish writing yet another novel and with any luck, sometime this year, finish writing the sequel to The Grave Watchers.
It's a full plate, but at least I've got a good enough head start on everything that I should wrap up on the timetable I've made up for myself.
That's one thing I can say about being a writer. You have to make a schedule for yourself. Set dates. Because if you don't give yourself goals, it can be very difficult to get things done. It's a job, you have to treat it like one. (The best job ever, but still a job).