When Shu Hattori started working at McKinsey & Co. in 2008, he constantly jotted down in a notebook insights into how to do his job better, harvested from his own experiences and by watching others around him. At one point, a colleague suggested the native of Britain and McGill University commerce graduate consider writing a book. By then, he had amassed about 70 principles drawn from the firm. He trimmed those to 47, which are featured in his new book The McKinsey Edge.