I have made it a policy to only comment on books that I like, but I make this book an exception because not only do I believe it to be a bad book, but one to beware of. The author is a very skilled and entertaining writer and he lists hundreds of scientific studies at the end that supposedly back up his claims. So most people will enjoy the book and accept the validity of his statements. Also he combines a number of statements that are quite true with others that are patently false, so it would be easy for those unfamiliar with the research (I am a professor of psychology) to consider all of his words to be valid.
Be careful of books that try to explain human behavior with one main principle (even 2, 3, or 4, for that matter)! There will inevitably be serious errors. Wiseman's "As if principle" is simple to understand: "If you want a quality, act as if you already have it." He argues that, for instance, if you want to be happy, then smile. If you want to be confident, then adjust your posture, clothing, etc, to look like a winner. He asserts that a behavioral response actually precedes and causes the emotional response, e.g., that it's not so much that we smile because we are happy, but that we smile, and then--our sensing our smiling, we conclude that we are happy. He gives another example of a fearful man fleeing from a bear--that his actions of fleeing, sweating, etc, evoke his conclusion that he is fearful.
In support of his principle, he quotes in detail the results of many studies. Thus he argues that something that approximates love can be induced in a laboratory setting by getting pairs of subjects to do the things that loving couples do, e.g., staring into each other's eyes and revealing confidential details. But this contrived situation does not justify his conclusions. Many/most people who spend some personal time with someone else will probably like them more. Another odd example is asking the reader to push the book away (supposedly "rejecting" it) and then hugging and kissing (supposedly "loving" it). He states that "research" (uncited) will cause people to have more positive feelings toward the book! I certainly did not have that reaction, and I'm pretty sure, that those who had a positive response lost it after a few seconds.
Wiseman's book omits the substantial evidence contradicting many of his claims. For instance, try to look happy to others when you don't feel like it. It generally won't convince them because it is extremely difficult to fake a smile. Unconscious nonverbal behaviors, such as the lack of any eye crinkling, will tell them--and yourself--that you are not all that happy. Smiling is much more than just turning the corners of your mouth up.
There is truth in the idea that actions can change emotions. Indeed it would be strange if running did not make you feel a bit more exhilarated or talking to an attractive stranger give you some pleasure. Clinical psyhologists do counsel their depressed patients to act as if they're not depressed--to get up in the morning, dress and shower, have breakfast, and be around friends. But hardly any therapist would believe that those actions would be sufficient, that a depressed person could or should "fake it til you make it." One must really look at the patient's emotional state and alleviate that, or in a few days, he just may stop getting out of bed---or worse. Real and lasting personal change must come from changing both one's feelings and behaviors, which have a dual, not a one-way , connection to each other.
And then there's the aspect of ability. Wiseman argues that to be creative, act in a novel way. Yes, that might help a bit, but that's a ridiculous oversimplification of how ability, background, and knowledge cause some people to be outstandingly creative.
But, of course, it's generally easier to change one's own behavior than one's abilities or feelings, which often run deep and have a long history. So many people will be tempted by Wiseman's simplistic solutions to believe that his advice will do them a lot of good.
Actually there is only a small amount of advice in this self-help book anyway. The great majority of his words are descriptions of studies.