In this chapter, Lamott talks about your "inner critic" or the "voice in your head." This is how she refers to the feeling of self-doubt or insecurity that authors can occasionally feel. It appears as if, despite her experience, Lamott is not immune to such doubts. In her text, she describes this process, and tries to help others overcome such doubts and concerns.
I believe taht she is successful in this task because she is able to accurately explain what that process is for the writer. Moreover, she is also able to describe strategies that allow us to get rid of such a critic.