In this stage, the tragic hero is missing something in his life, and he might look for some "unusual" way to gain satisfaction. The nameless narrator of "The Black Cat," doesn't tell us that anything is missing from his life, but he does take up drinking. We don't know why he started drinking, and we don't know exactly when he started, though paragraph 13 suggests that it was when he got Pluto and the other pets. Drinking isn't exactly unusual, but it is what the narrator seems to "anticipate" or look forward to in this first stage of the story.
In this stage the hero "becomes in some way committed to his course of action," and things seem to be going extraordinarily well for the hero. In "The Black Cat," we know that the narrator's drinking goes on for several years. He seems to stay drunk most of the time. Those years of drunkenness probably did pass by in a dream, though we can't say that things were going well. In fact, his life sounds more like a nightmare than a dream. But Booker has a separate stage for nightmares, which you'll read about very soon.
For a time, Pluto was the only one in the family to escape being physically abused by the narrator. Things start to go wrong for the narrator when he turns on his once somewhat beloved pet. After cutting out Pluto's eye, and then hanging him, the narrator's house catches on fire, and the family loses everything. Booker says that in this stage "a 'shadow figure' might appear […] to threaten" the hero. This would be the second cat…
After the second cat appears, the narrator doesn't mention drinking again. We don't know if this is because he stopped, or because he becomes so obsessed with the cat that he just doesn't bother to mention it. The cat sticks to him like glue, even sitting on his chest and breathing on his face while he's sleeping. He calls the cat a "Night Mare" (21). (Check out "Symbols, Imagery, Allegory" for more on the "Night Mare.") Like most tragic Booker heroes, everything in the narrator's life is out of control in this stage. So out of control that the narrator kills his wife and hides her body in the wall of the cellar.
In this stage, the hero does something to ensure his own "destruction" or death. After the narrator hides his wife's body, the cat disappears and he feels free and calm. When he gets too sure of himself and bangs on the wall hiding the corpse, he rouses the cat, (who was walled in with the body) exposing his hiding place to the police. He's arrested and sentenced to death.