Everyone gets something different out of a book. The opinions here are mine only.
The basic premise of the book is that many techniques prescibed in self-help books and programmes rolled out to address social problems lack proper scientific validation and have not worked. Many such programmes (e.g. to reduce prejudice, alcohol and drug abuse, close the achievement gap) have been implemented without rigorous testing, therefore have wasted billions of dollars and have not worked. Timothy Wilson criticises the use of testimonials by those who advocate such techniques as biased, and recommends strict scientific methods, with control groups etc. to test techniques used for social problems just as is done in medicine (because common sense arguments, although appealing, often lead to wrong conclusions).
Wilson advocates a a number of tested techniques (such as “story-editing” or redirecting the internal narrative, labelling kids’ behaviour appropriately, distancing and writing for trauma victims and other techniques) instead, to effectively deal with these problems.
I like the rigour Wilson requires and applies to the testing of the techniques to achieve objectivity, as opposed to using glowing testimonials, which are possibly biased. However, Wilson himself states that it is unclear whether applying these laboratory tested techniques in the real world will achieve the same results – there are too many complexities; however, at least it is a step in the right direction.