By collecting fieldstones (little ideas) and polishing/rewriting over time whenever one feels strongly about a particular subject, one is able to draw on an existing collection of partially-written drafts on diverse topics that can be deployed quickly. Or combine several similar ideas and deploy a more polished/comprehensive treatment of a subject than would be possible with an on-the-spot piece.
It also accounts for the fact that our interests shift. I don't know about others but I often get into phases where I become intensely interested in a subject, research it to heck until the interest peters out. I was once really interested in the topic of alleviating loneliness because I was profoundly affected by it. I'd written many fieldstones on the topic, and contemplated it a lot. If I were given a task to write about loneliness right now, I'd probably struggle because I'm no longer as intimate with (nor as interested in) the subject as I once was, but with fieldstones I can draw on all the (partial) analyses I'd done when I was in that phase.
The fieldstone method is more than just about taking notes -- it's about brewing them over time based on one's feelings.
But, as I say, I agree in general and it's one reason I like to start out in Scrivener for biggest projects. It lets me pull in research and start working on some bite-sized chunks related to that research (or other material) rather than trying to craft some grand narrative starting from a blank sheet. (The narrative hook can be the hardest thing to come up with so it may very well not be what you want to start with. (You'll probably throw it out anyway.)
Absolutely fantastic books by they way.I still recommend Secrets of Consulting to every CS graduate I meet.
I find that I have more stress from concern about whether the writing really is moving forward even when I'm putting words on the page - i.e. will the words I'm writing 'work' - than from writers block. Always at the back of my mind is will these words make the work less cohesive - am I moving backwards?
But in general we manage what we measure and we normally have a word count but no easy way to measure whether a work is really coming together.
If you're feeling a block, then first work around the work, eventually you'll be working ON the work.
In a nutshell, the book describes how the act of writing can be broken down into many stages: sometimes you are collecting "fieldstones" (i.e. research), sometimes you editing, and sometimes you are synthesizing. Regardless, there's always something to do that moves you forward.
* Field stone method - https://geraldmweinberg.com/Site/On_Writing.html