Good answer, Cyrena. The difference here is that only one person is interested in saving he marriage. So we have the LBS who used to be sad and clingy, and begging for another chance suddenly acting all happy and getting a life and not arguing with the WAS. If the LBS gives the book to the WAS, then the WAS sees that they are just following advice from a book and thinks that all the changes are fake. No one wants to come back to fake changes. Hence the advice -- don't show the book.
