And from what I heard, Joseph contributed much to his deterioration, by a narrowminded partiality which prompted him to flatter and pet him, as a boy, because he was the head of the old family.
Then personal appearance sympathised with mental deterioration: he acquired a slouching gait and ignoble look; his naturally reserved disposition was exaggerated into an almost idiotic excess of unsociable moroseness; and he took a grim pleasure, apparently, in exciting the aversion rather than the esteem of his few acquaintance.
There are no more uses of "deteriorate" in the book.
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The situation could quickly deteriorate.
Writing, at its best, is a lonely life. Organizations for writers palliate the writer’s loneliness, but I doubt if they improve his writing. He grows in public stature as he sheds his loneliness and often his work deteriorates.