At the End of a Procrastinated Day
The Hemingway Trick: Stop in the middle.  Never stop working at the natural barriers.  They next time you start working, the barrier will be the first thing you encounter, and you won't have the momentum to overcome it.  Try to stop writing mid-chapter, or mid-sentence (or mid function). Know how to finish, but stop working. The next time you start, you know exactly what needs to be done. There will even be the urge to start working to finish the unfinished.Nearing the end of a unproductive day, accept that the day was not productive, start on what you will work on tomorrow, do a little, and stop in the middle.