What was the most difficult book to understand in the world?

This question is difficult to answer because the difficult books in the world vary from person to person. Everyone's cultural background, reading experience, and knowledge level are different, so it is difficult to determine which book is the most difficult. However, some classic literary works were widely regarded as difficult to understand, such as Dream of the Red Chamber, One Hundred Years of Solitude, The Kite Runner, and so on. These works had profound cultural implications and unique narrative methods. It might be difficult for readers without relevant backgrounds to understand.