This paragraph is located within the section about the “many exotic new facts” (200) that one could learn if they ever had the chance to visit Ennet House. It is referring to Tiny Ewell, the “elf sized U.S. male” resident of the halfway house whose substance of choice appears to have been alcohol, and picked up an obsession with other residents tattoos once his enslaving Substance (note the capital S) was removed from his life.
Obsession is defined as a compulsive preoccupation with a fixed idea, feeling or emotion, often accompanied by symptoms of anxiety. Addiction is to become physiologically or psychologically dependent on a substance. Obsession is mental (needing to wear a specific item of clothing in order to play your best in a tennis match, or compulsively asking everybody around you about the background behind all of your tattoos), while addiction is physical (withdrawal symptoms when the substance hasn’t been used in a while, or a crushing need for the biological response associated with the action e.g. endorphins, adrenaline, etc.), but both are characterized with the need to complete a specific thought or action in order to receive a “reward”, or prevent the “punishment” of not thinking or acting. Nearly every character in Infinite Jest has either an addiction or an obsession, if not both.
Tiny Ewell first had an addiction. In the absence of Tiny’s Substance, he uses his obsessions of tattoos, of the definition of alcoholic, even of cookies and the ways residents make their beds, to continue using cyclical and destructive “addiction” thinking, causing him to spend all of his time thinking, analyzing and overanalyzing his obsessions, and thus ignoring that he has a problem, which is hampering any true improvements. He is protecting himself, with his enforced lack of awareness and obsessions, from the fallout that would result with him realizing that he does have a problem, and that he has earned all consequences resulting from his actions. His wife had changed the locks and filed a restraining order due to him. He ended up in the Ennet halfway house due to his own actions. He is no better than anyone else in Ennet house, despite his prestigious credit card, educated vocabulary or lack of tattoos. This revelation, which Tiny is likely aware of, on some level, would break his sense of self, and he is terrified of that, so he falls into the only kind of destructive behavior he has access to, emphasizing Wallace’s point that addiction and obsession are mirror images, equally dangerous and destructive to the self, despite the lack of a Substance.