I would argue that writing a book about what you know, or summarizing your knowledge so that it is useful for other people, is working outside of your comfort z

I would argue that writing a book about what you know, or summarizing your knowledge so that it is useful for other people, is working outside of your comfort zone. If you can explain something to a 5th grader, you probably know it pretty well. The fact that they said they could never do it indicates that they should probably focus on that.