Most SH are thus named because their authors help themselves to their victims' money. Even good books are only good for readers who already know that the kind of advice given is the one they need. What the other posters said.

If you are asking us about the value of "positive thinking": whenever it is preached as an imperative, it has already gone wrong. If we adopted that ideology, we would probably feel that our failure to ignore our failures just adds a new one to our perceived failures.