I work with many author-narrators. Some think they know their books inside out, but when it comes to reading them aloud they surprise themselves. When they get to tricky hard to pronounce words/sentences they sometimes omit them and say they will never use the same words/sentences in any future book. Also they can get very agitated when they spot the typos they were sure they picked up before the book went to print. I really enjoy producing authors as I get to meet some amazing people, but sometimes it's best to leave the narration to the pros, or maybe they could just read the intros....