One thing I am thinking about now is that, for me, inspiration can be present or absent on many levels, from "knowing what I mean to convey" (in terms of plot, mood, meaning, build-up/pay-off...) to "picking the right phrasing". Sometimes both arrive at once, phew. Sometimes I know what I want to say but my language is not cooperating at all. And sometimes I find it easy to write sentences or even paragraphs that feel good, but the overall piece feels pointless and incoherent... (That's when the usual writerly advice of "killing your darlings" comes in handy.)
For a longer piece, the different levels of inspiration can wink in and out of existence at random, so I have to get over little bumps of various types.
(There were only a couple of Yoinktober pieces where I didn't have an overall idea -- when I didn't have one, I generally didn't write at all -- but a lot of them have failed to convey what I wanted. Communication is hard, mrr.