We don’t always know what we think we know. Confirmation bias (your brain’s tendency to cue into, or seek out, information that confirms opinions you already have), the Dunning-Kruger effect (your overestimation of your competence), subjective validation (your tendency to believe vague, positive predictions) – each of these unlocks some quirk of the human mind, some way in which we misperceive the world.

In his entertaining new book, You Are Not So Smart: Why You Have Too Many Friends on Facebook, Why Your Memory Is Mostly Fiction, and 46 Other Ways You’re Deluding Yourself (Gotham, 2011), journalist David McRaney has collected such well-established theories – many of them culled from his blog of the same.

It is enlightening to see all the mistakes we’re apt to make in one handy volume: how we attribute meaning to coincidences (apophenia); how we re-create our memories differently each time (misinformation effect); and how our brain effectively limits us, by evolution, to around 150 friends (Dunbar’s number) – making most of those people on Facebook mere acquaintances.

There are reasons for these mental miscalculations, as McRaney points out. His book deals with three kinds: cognitive biases, which help us maintain a positive image of ourselves; heuristics, which are mental shortcuts that improve cognitive efficiency; and logical fallacies, which occur when our crucial powers of deduction overstep their bounds.

All these things can lead us to bad choices and false conclusions, which McRaney fleshes out in each chapter. Some sections may change how you see the world, and others may change how you see yourself. Many will leave you wanting to know more. “In the modern world,” McRaney quotes Bertrand Russell as saying, “the stupid are cocksure while the intelligent are full of doubt.” You may not be any smarter when you finish this book, but you will have begun to wonder how smart you really are. And that is the beginning of true intelligence.