Here’s why trusting yourself is important: to write nonfiction, you need to have an angle — a slant, or a point of view, if you will. New writers haven’t developed trust in themselves, so they want to conform. This is death to your nonfiction — forget conforming. You don’t want to write an endless series of “me too” books. Your ideas, opinions, skills — everything that makes you who you are — are valuable. Use what you are.
If you have a point of view in total opposition to what everyone believes about a topic you may write a very popular book. Don’t go out of your way to be contrary or controversial. But if you have an opposite point of view to perceived wisdom on a topic: you believe what “everyone” thinks is wrong-headed, go with it.