“Why on Earth are people still buying a self-help book from 1936? Carnegie’s principles of relentless positivity are right at home in a culture of ingratiation, from the widespread drive to amass online friends by liking their posts (and thence to become an influencer) to the way every interaction with someone in the service industry feels like the prelude to a customer satisfaction survey. His ideas retain a startling currency in a society whose very drives and mores he helped to create.”