Jim Collins’ Built to Last was one of the best business books of the past two decades. One of the more intriguing ideas it contains is “the Stockdale paradox”.

James Stockdale was the most senior American serviceman to be captured during the Vietnam war. (He ended his career, sadly, as the inept vice-presidential candidate in Ross Perot’s quixotic attempt to win the presidency in 1992). Over seven years of captivity, Stockdale suffered repeated torture and beatings at the hands of the Vietcong.