A writer looks until the thing stops being generic. What moved? What made the sound? What shape did it have? What was it made of? What is it called? If you do not know the name, find it. A vague adjective is not a substitute for having looked.
The sentence can be part of the looking. It can reveal a distinction you had not made, expose what you do not know, or force a thought past its first approximation. But a sentence does not become right because it sounds finished. It remains open to correction by what the writer discovers. Fluency can hide the need for that correction. The words may settle into place while the observation is still vague or the thought has not gone far enough.
A good sentence is not the same thing as the capacity to write well. Writing well requires the ability to notice distinctions, recognize when the words claim more than the observation or thought supports, and revise accordingly.
AI makes that distinction unusually clear. It can produce fluent, convincing sentences. But fluency alone does not show that anything has been examined closely, distinguished accurately, or thought through. Generating language is therefore only part of what writing well requires. A sentence can be finished while the observation remains vague or the thought incomplete.