Stumbling on Happiness is a nonfiction book by Daniel Gilbert, published in the United States and Canada in 2006 by Knopf. It has been translated into more than thirty languages and is a New York Times bestseller. Theme Gilbert's central thesis is that, through perception and cognitive biases, people imagine the future poorly, in particular what will make them happy. He argues that imagination fails in three ways: Imagination tends to add and remove details, but people do not realize that key details may be fabricated or missing from the imagined scenario. Imagined futures (and pasts) are more like the present than they actually will be (or were). Imagination fails to realize that things will feel different once they actually happen—most notably, the psychological immune system will make bad things feel not so bad as they are imagined to feel. Also, Gilbert covers the topic of 'filling in' or the frequent use of patterns, by the mind, to connect events which we do actually recall with other events we expect or anticipate fit into the expected experience. This 'filling in' is also used by our eyes and optic nerves to remove our blind spot or scotoma, and instead substitute what our mind expects to be present in the blind spot. The book is written for the layperson, generally avoiding abstruse terminology and explaining common quirks of reasoning through simple experiments that exploited them. Summary Stumbling on Happiness has six sections labeled Prospection, Subjectivity, Realism, Presentism, Rationalization, and Corrigibility. A summary of each follows. In the Prospection section Gilbert contends that humans are most special because of their ability to imagine. Our large frontal lobes biologically distinguish us from other animals and the function of the frontal lobe is to help us imagine. However, our imagination often leads us astray, and the purpose of the book is to help the reader appreciate the shortcomings of imagination. The Subjectivity section addresses the meaning of happiness and emphasizes that happiness is a subjective feeling. Gilbert says, “Evaluating people’s claims about their own happiness is an exceptionally thorny business.” No perfectly reliable tool exists to measure a person’s happiness. Instead researchers must rely primarily on the “honest, real-time report of the attentive individual”. Finally, given the imperfections in self-reported feelings of happiness, scientists must rely on the law of large numbers, namely, to ask many people the same question and compare their answers. The