Finally reached Z and this was another struggle until I hit upon Zeal. Every writer has to have this when they're starting, finishing or revising a story. With out that bit of excitement, the book slows to a halt. It's the enthusiasm you bring to your story that makes the journey worthwhile.
I've known writers who have lost this quality. The reasons are many. Poor health that keeps the writer from the computer. Not having sales of their stories. Receiving a poor review can slow a writer down.
What a writer must do is find that zeal. One of my ways is to look at each story as a new adventure. When I write the end, the story I send off is done and so am I - with that story. What happens to is is up to the gods of writing. The new story is the all.