As the sentence progresses, some of its demands are satisfied, others deferred, others complicated, and meanwhile new ones arc created.
I think this is the hard part of grammar and writing. A sentence can be complete yet complicated at the same time. The structure of a sentence adds more dimension to it and the way a writer develops their thoughts can change mid-sentence. As thoughts change so does the structure of a sentence. One moment you have a basic sentence with a subject and predicate that turns to a complex one with multiple clauses as words are added. This is the beauty of writing.