Question from a book fan

The film is about them trying to conceive, deciding to go for ivf and then writing the programme. If I remember rightly, the diary only comes into it when Sam reads it to add more emotion to the female character. I haven't seen it in a while though, so I may be wrong.

Elizabeth! Hide the rum.

I know this was made a while ago, but I just finished reading the book. Surely you must know that the film is produced in relatively the same way Sam writes the film in the book? I don't understand how this concept would be hard to understand..

You look pretty
What?
er I said you look *beep*