What System One did is apply a simple rule of thumb: If examples of something can be recalled easily, that thing must be common. Psychologists call this the “availability heuristic.” Obviously, System One is both brilliant and flawed. It is brilliant because the simple rules of thumb System One uses allow it to assess a situation and render a judgment in an instant—which is exactly what you need when you see a shadow move at the back of an alley and you don’t have the latest crime statistics handy. But System One is also flawed because the same rules of thumb can generate irrational
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