I Will Never Believe That Sarah, It Was a Real Person

A book is structured as a conversation to an imaginary person who acts as a sounding board for the author. This device can be used well, but it strikes me as often a device that is used by people who are not the strongest of writers. And so it's a crutch. It also then makes the imaginary person, I don't think authors who do this can resist. The bugbear that always gets me about this is the imaginary characters will almost always just obsessively use the author's name.