“The Book of Sand” by Jorge Luis Borges.

One of the character's internal struggles in "The Book of Sand" is the narrator's struggle with obsession and the fear of losing himself. After encountering the book that never ends, the narrator becomes infatuated with it and cannot resist its allure. He spends hours upon hours reading it, unable to put it down. However, this obsession slowly consumes him, causing him to neglect his work, relationships, and even his own self-care. The narrator becomes isolated and loses touch with reality as the book becomes his sole focus. This internal struggle with obsession forces the character to question his own sanity and confront the fear of losing his sense of self in the face of an all-consuming obsession.

Another internal struggle is the narrator's struggle with the existential dilemma of infinite possibilities. As the narrator delves deeper into the Book of Sand, he realizes that its pages are infinite and contain every possible combination of words and stories. This revelation overwhelms him with a sense of insignificance and meaninglessness. The concept that there is no end or order to the book makes the narrator question the existence of individuality and purpose in life. He grapples with the absurdity of trying to find meaning in a universe of infinite possibilities, leading to an internal struggle that shakes the very foundations of his worldview.