How is it that no-one ever makes a mistake on purpose, but that mistakes get made? This is one of the questions that Edward de Bono answers in this book. His theme is everyday thinking, how the mind actually works - not how philosophers think it should work. Dr de Bono has based his book on a direct and practical experiment - the Black Cylinder Experiment - and the conclusions of the one thousand people who took part provide the backbone for this study. With the results of the experiment at hand, the author explores the four practical ways of being right: currant cake (emotional rightness); jigsaw puzzles (logical lightness); village Venus (unique rightness); measles (recognition rightness). In addition, he picks out and names the five levels of understanding and the five major mistakes in thinking.