I felt obliged to answer a valid question from a reviewer: "if we are so stupid (and the book has lots of evidence that we can be) then how come we are so clever (after all, there is lots of evidence for that, too). In fact, more than that, why is it that we can look so stupid floundering about trying to find the answer to a problem which in a differently phrased, but formally identical, form is trivial?"
It is perhaps an understandable question, and someone like Robert Cialdini answers that part in more detail.
To really, truly understand the human animal there is no other way than delve into our evolutionary past and look at how we evolved and what forces shaped us. And maybe have a functional idea of the discipline of economics.
Undoubtedly more "autistic" types have sprung up here and there but most of them have not been particularly succesful at spreading their genes through the gene pool so that we all possess such "savant" skills.
Problem is that a living organism like a human need to be balanced on so many levels in order to survive. So we don't evolve super computer calculating minds, nor do we evolve only the ability to run faster than anybody else. No, we have an adaptive mix of traits/abilities.
Furthermore no one person can know everything, and no one person is likely to be very succesful if he has to figure every single thing out for himself.
So succesful humans - those "fit" according to Darwinian terms - have developed a wide range of rules-of-thumb. E.g. we tend to inately trust the judgement of a group of our peers: "everyone does it", "one million sold already" and "I'm so relieved to discover I'm not alone (with my illness, my sexual preference, etc.) This explains why the logical fallacy "argumentum ad populum" is so prevalent (as _scientists_ know truth is a not democratically decided, but we are so very conditioned genetically to accept as true the concerted action of _many_ other peers).
To the slightly autistic economist it may be incomprehensible that someone doesn't just play the game according to it's clearly defined payoffs. The economist can't really figure out just why it should be so important whether the word "loss" is used when the bottomline is the same. However, to humans it is not unlikely that these theoretical games become lethal when you LOSE food. So in the economist game this rule of thumb fails us, but survival-wise this rule has actually kept us very much alive and well for the most part.
BTW - you may get the impression that we're indeed "stupid", but think for a second and tell me if you are not simply falling prey to the nasty availability bias? ;)