According to today's article, Self-Help books that tell you to repeat mantras like "I am a lovable person" do not work for people with low self-esteem, (LSE) and only marginally work for those with high self-esteem (HSE).
I suspect they don't work for those with LSE because as they're chanting those they're thinking about how they're not true. It brings to the forefront of their minds how much of a lovable person they're not. Then they feel worse.
I suspect the reason a great many other self-help books don't work is that people who read them don't actually put them into practise. Reading a book won't fix your life. Doing what the book says might. Years ago I read The Wealthy Barber - a small, easy to understand, book about finances. I have yet to do anything suggested in that book.
Will Ferguson wrote a novel called "Happiness" about a self-help book that actually works. Everyone gets rich, looses weight, follows their dreams, and embraces the things they can't change. Hilarious.
BTW: Today's title is one of the best lines from the movie School for Scoundrels with Billy Bob Thornton and Jon Heder (a.k.a. Napoleon Dynamite).