Why did Edgar Allan Poe have the narrator kill the old man on the eighth night in 'The Tell-Tale Heart' what symbolism does the eighth night represent?

Edgar Allan Poe likely chose the eighth night as a narrative device to build tension and emphasize the narrator's escalating paranoia and guilt. The number eight in some cultures is associated with infinity or completeness, which could symbolize the narrator's final descent into madness and his inability to escape the consequences of his actions.