While I’m specifically speaking about story writing, this is such a broadly applicable principle, that it could be placed into any category. When I speak of Ebbs, I mean those moments where you focus on understanding the underlying process. Flows are exactly what they sound like, everything is moving at a good speed.
For writing, I’m currently doing three things: writing in Scrivener on my Mac, writing in Daedalus on my Phone, and reading about how to be a better writer. Daedalus syncs to Scrivener via Dropbox, and I primarly use the phone to take notes and/or work on chapters. Scrivener is meant to be my production tool, but I find that most production takes place on the road, and I rather expect to do the finalisation on the Mac when the time is right. As well as maintenance / the act or prettying up, of course.
The Ebbs, to me, are contained within the transitions. There is a switching cost, to use a fancy term, that happens after you spend time in the Flow, suddenly come to a halt, and when you find yourself reorientating / searching for next starting point.
Very practically, I hate the way Dropbox syncs between these two softwares, creating duplicates, requiring some hacking in Scrivener, and a better understanding of that process overall. That is an inefficiency (Scrivener!), which creates an Ebb.
The other Ebb is new learning about production, during production. There is much to learn about writing, I find, specifically when it comes to narrative development and writing for the purpose of being read. Those pieces of knowledge force me to bring the writing to a halt and introduce new orientation points. Similarly, Scrivener had a learning curve in the sense of organising chapters, character backgrounds, etc., that I had to get past.
All of these are excuses of course. A writer should just write, and I often find myself wondering does a Steven King, Paul Auster, or a Nick Hornby do just that? Some interviews that I read suggest that they too struggle and often a good writing day is two good hours of writing, rather than the mystical 9-5 production mantra.
Flow could rather be described as the ability to navigate past the Ebb, wether through practice (likely) or outsourcing (possible). Food for further thought.