The time comes when writer stops thinking that he or she will never manage to sort out the mess that is the first draft of the current work in progress, and begins to see a point in time, in the not too distant future, when it will be finished.
It's an exciting time, because one can look forward to having a new book published, and to starting another one.
The only difficulty is deciding what to write. One of the advantages of being self-published is that one can choose for oneself, without having to worry about whether a particular genre or subject is currently considered marketable.
On the other hand, it can be a disadvantage, because one has to decide for oneself, without the benefit of discussion with an agent or editor who knows about trends in book buying, and about what else is due to be published in the next year or so.
A self-published writer cannot - or should not - wait to see how the current work in progress will sell before deciding what to write next; in digital self publishing, the emphasis should be on getting the next book out as quickly as is consistent with quality, so that readers don't forget one's name.
So, should I write another book about this set of characters, or that set of characters? What about another standalone, similar to the already published one that's been doing quite well? Or that new genre and pen-name I've been thinking about?
Or I could start work on one of my shiny new ideas.
Of course, there is always a shiny new idea to distract the writer away from the work in progress. I have a lot of respect for writers such as Dorothy Dunnett and J. K. Rowling, who conceived multi-volume sagas with ongoing storylines and saw them through to the end - in J. K. Rowling's case, while also dealing with the demands of a new marriage and new babies, overseeing the production of the films, and worldwide fame.
Realistically, I know that the shiny new ideas (currently three of them) need a lot of thought and planning before I can begin writing. While I know the characters and settings, I have no idea of plots!
Of course, if one listened to the doom-mongers who claim that the e-book boom is over, and the Kindle is dead, one wouldn't bother to write anything at all. But the ideas would still be there, so why not write them down and put them out there?