“Happiness is beneficial for the body but it is grief that develops the powers of the mind.”
Marcel Proust book In Search of Lost Time
Le bonheur est salutaire pour le corps, mais c'est le chagrin qui développe les forces de l'esprit.
Source: In Search of Lost Time, Remembrance of Things Past (1913-1927), Vol. VII: The Past Recaptured (1927), Ch. III: "An Afternoon Party at the House of the Princesse de Guermantes"