I've been gradually realising this, but hearing it from someone else phrased so perfectly really makes it stick. A huge cause of my lack of productivity last year was this confused and abstract feeling like something was missing in what I was doing, and that it had to be "figured out" before I could move forwards. It's like chasing a feeling of completion and perfection, except that the chase doesn't particularly involve creation, only endless webs of thinking. So I guess I just need to do stuff.
(I guess I know I've told myself that so many times before - I unfortunately possess this habit of having the same epiphany, over and over again, and never taking my own advice, so in an hour or so, or whenever I next decide to start working, I'll be back to thinking, "Hmm, I could make more work, but first, what is missing...")