From the opening paragraph of Yu Tsun's narrative and his frequent use of the word "implacable," we get the impression that he's a big believer in fate. He searches for omens and signs, regards his death as impending and unavoidable, and thinks of the future as a fact "as irrevocable as the past." When he meets Dr. Albert, he seems to have met a fellow believer – the two discuss Ts'ui Pen's life as though it had been written according to destiny. The contents of Ts'ui Pen's novel force us to reflect on that idea. On the one hand, the notion of infinite futures suggests that each individual narrative would have the appearance of being fated, as it must follow an order of events not repeated in any other time. On the other hand, the excerpts that Dr. Albert reads from Ts'ui Pen's book suggest that certain outcomes will occur no matter the circumstances that lead to them.
Yu Tsun's technique of "impos[ing] upon himself a future as irrevocable as the past" allows him to accomplish his abominable tasks without feeling guilt. The consequences of his actions are predestined, he believes; he is merely an instrument of their realization.
Borges is intentionally ambiguous on the matter of destiny. In telling the story through the perspective of a narrator who believes in fate, he is able to simultaneously create an ominous mood in which coincidence seems preordained and also allow his reader to doubt the narrator's perspective and its mystical implications.