Straight from… Reddit
Is it possible to write a novel with only a narrator and no characters?
Answer: You can certainly do that. The problem is keeping your piece engaging. Character reflection can only go so far, and without action and interaction readers can get bored easily. If you only have one character you take the risk that, if the reader doesn’t like your character, you’ll ruin the entire book for him. Even memoirs and autobiographies include other characters.