There was no definite answer to this question because there were many ways to define the most difficult book in the world. Different people would have different understandings of " difficult ". Some people might think that The Theory of Relativeness is a difficult book because it involves advanced knowledge of physics, while others might think that Harry Potter and the Sorcerer's Stone is a difficult book because it contains a lot of magical elements and fantasy plots. Therefore, it was impossible to determine which book was the "most difficult book in the world" because it depended on the reader's personal background and reading experience.