Most bookshops have a large section devoted to all aspects of self-help. I was seized by indecision when trying to choose a book on effective decision-making and came away empty-handed. On another occasion, an assistant tried to recommend a book on overcoming avoidance, but I gave it a miss.
Oh, all right, these are imaginary scenarios for purposes of comedic effect. But I did once return a self-help book on assertiveness and got a full refund. I think that must be the ultimate test of effectiveness, and it also poses a nice philosophical conundrum:
not effective – unable to return book – grounds to return it
effective – able to return it – no grounds to return it