Yesterday, I read cover to cover, "Healing the Sensitive Heart" by Debra Mandel, PhD. After reading this book, I had a revelation: I finally realized that I never felt that my parents loved me (they were very critical) and then so many N pieces fell into place. When you don't feel unconditionally loved by a parent, you can grow up to feel inherently flawed and this can cause shame, which permeates your adult life. Then, you can go thru adulthood seeking the unconditional love you never received from your parents.
IMO, the book puts together all the pieces of the N puzzle: not loving ourselves, not having good boundaries, being criticized as children, shame, humiliation, accepting that we can only change ourselves, walking away from relationships with people who refuse to change, etc, etc. IMO, Dr. Mandel interweaves all the pieces together, shows us why we've been victimized by & attracted to Ns and then shows us how we can create a life in which we can thrive. Although she never talks about Ns, she clearly refers to Ns when she discusses those people who invalidate us.
While her presentation does not provide new information, it's the way she presents the info that is so helpful and easily digestible.