The study of human nature, ‘the observation of the human heart and its passions,’ was his constant preoccupation. But where could he study the passions better than in himself? Though he lived exuberantly, submitting himself to experience... he went on incessantly writing down everything that happened to him just as it happened… he even led to perform some remarkable experiments upon himself…He laid claim to having been a soldier, a man of fortune, a great lover, a society wit, a diplomat, a traveler, and even, sometimes, a revolutionary conspirator…