Defining what entails a meaningful life has preoccupied philosophers from Plato and Aristotle to Simone de Beauvoir and Iris Murdoch. Surveying centuries of thoughtful chin-tugging about the human condition, Kieran Setiya identifies a broad trend: “an affinity with ‘the power of positive thinking’ that implores us not to dwell on trials and tribulations but to dream of the life we want.”