Think of all the men who go on believing in the love of a mistress in whom nothing is more flagrant than her infidelities; of all those torn between the hope of something beyond this life (such as the bereft widower who remembers a beloved wife, or the artist who indulges in dreams of posthumous fame, each of them looking forward to an afterlife which he knows is inconceivable) and the desire for a reassuring oblivion, when their better judgment reminds them of the faults they might otherwise have to expiate after death; or think of the travelers who are uplifted by the general beauty of a journey they have just completed, although during it their main impression, day after day, was that it was a chore—think of them before deciding whether, given the promiscuity of the ideas that lurk within us, a single one of those that afford us our greatest happiness has not begun life by parasitically attaching itself to a foreign idea with which it happened to come into contact, and by drawing from it much of the power of pleasing which it once lacked.