You hear athletes - and particularly marathon runners - talk about breaking through the pain barrier. Well, I reckon the same thing applies to writing a novel. Writing the last 10-20% involves more work than the first 80-90%, and there does come a time or three when you feel it's all become too much.
One problem I have is that I often end up with chunks of existing writing which I'm having to rewrite to fit into the plot as it now stands. Facing 2000 words of text in which the wrong characters say and do the wrong things to a version of the plot you discarded two months ago is not my idea of fun. However, if I break the 2000 word scene into the smallest possible units and tackle them one by one, it's much easier. I mean, how hard is it to rewrite a sentence or a paragraph?
Another issue is the drag of That Which Has Gone Before. Usually, multiple versions of it. Deep down I know I'll tidy it all up during the second draft, but at this stage my mental picture of the novel is that of 100+ dimly-remembered scenes, some of which have long since been discarded.
(That's a very good reason not to start rewriting until you get to the end of the first draft. Going through the book with all the later events more-or-less clear in your mind allows you to emphasise bits of the plot which foreshadow the ending, and submerge - or cut - the rest.)
Anyway, I can see the end now and the pain isn't as bad as I thought ;-)
Simon Haynes is the author of the Hal Spacejock and Hal Junior series (Amazon / Smashwords / other formats)