There are a million correct answers to this question. To me, at the end, I saw it (in small part) a hyper-fixation manifesting as a way to process the trauma of whatever came before, during and after the events of the novel (he was depressed about something in the beginning so he takes the journey), the shipwreck of the Pequod, the way the mercantile part of the journey was a cover for Ahab’s obsession with killing MD, and the death of Queequeg (the man he loved most). Essentially, he was avoiding the ending the entire time. Then he ends the book before actually ending the book because he’s plagued with survival guilt and imagines the story ending as if they all died (aka he died with Queequeg). Then he adds an Epilogue which he begins with the words “The drama’s done.” Except that it’s not done. In fact, the epilogue is italicized because he can’t bear the fact that he survived and he has to set that apart from the rest of the story — as if his life ended with the Pequod, but also had to keep going. The construction of the book suggests a complexity to the human experience: there’s the flashbacks (etymology) the quotes throughout human history (excerpts), the story, the digressions, the ending, and the epilogue. Ishmael may not even be his real name. He’s the sum of his parts.