The novice writer's "natural tendency as a writer is to think primarily of himself--hence to write primarily for himself. Here, in a nutshell, lies the ultimate reason for most bad writing. He isn't aware of his egocentrism, of course, but all the symptoms of his root problem are there: he thinks through an idea only until it is passably clear to him, since, for his purposes, it needn't be any clearer; he dispenses with transitions because it's enough that he knows how his ideas connect; he uses a private system--or no system--of punctuation; he doesn't trouble to define his terms because he understands perfectly well what he means by them; he writes page after page without bothering to vary his sentence structure; he leaves off page numbers and footnotes; he paragraphs only when the mood strikes him; he ends abruptly when he decides he's had enough; he neglects to proofread the final job because the writing is over . . . Given his total self-orientation, it's no wonder that he fails repeatedly as a writer. Actually, he's not writing at all; he's merely communing privately with himself--that is, he's simply putting thoughts down on paper." - John R. Trimble, Writing with Style: Conversations on the Art of Writing (3rd Edition) (Prentice Hall, 2011), 3.
The paragraph strikes me as a particularly good description of a lot of beginning college composition, but I'm reading the book in the hope that it will help my own writing. So far Trimble's book is as bracing and brilliant as James M. Lang said it would be. Tolle Lege!