A classic example is the splitting of the uranium atom. Until 1938, the world’s top physicists carried the unexamined assumption that atomic nuclei couldn’t be split into two. This left them baffled for several years by the strange results observed when uranium was bombarded with slow neutrons. What was going on? Finally Lise Meitner and her nephew Otto Frisch worked it out between them, and told Niels Bohr. “Oh, what idiots we all have been!” was his instant, forehead-slapping response. Some say the real stupidity at that point was telling the politicians and generals, and it is certainly true that wars regularly offer particularly chilling examples of the results of stupidity, but so many of the other sources of misery in the world could be ameliorated if only we were a little better at spotting the flaws in our own reasoning and beliefs.