Is there anyone left who’d still be mortified to have it known that they’d purchased, or maybe even benefited from, a self-help book? In recent years, the genre’s gone mainstream: Jordan Peterson’s 12 Rules for Life bestrides the bestseller lists, alongside titles on the Danish, Finnish and Japanese secrets to health and happiness, and the life-changing magic of tidying up; Alain de Botton embraces the label, while most ‘big ideas’ books, from Malcolm Gladwell to Yuval Noah Harari, are at least partly self-help in disguise.