"They use their characters as mouthpieces for what they want to say or hear."
Let’s skip ahead to chapter nine of Steering the Craft, which is chock full of rich and useful information. This chapter is on “Indirect Narration, or What Tells.” Here’s the bit that leapt out at me:
If all people in the memoir say only what the author wanted to hear, all we hear is the author speaking–an interminable monologue. Some fiction writers do the same thing. They use their characters as mouthpieces for what they want to say or hear. And so you get the story where everybody talks alike, and they all talk like the author.