If it's all instruction, you get annoyed with it and bored,...

If it's all instruction, you get annoyed with it and bored, and you stop reading. If it's all entertainment, you read it quite quickly, your heart going pitty-pat, pitty-pat. But when you finish, that's it. You're not going to think about it much afterward, apart from the odd nightmare. You're not going to read that book again.