Rejoicing in our joy, not suffering over our suffering, makes someone a friend.
(Friedrich Nietzsche (1844-1900), German philosopher, classical scholar, critic of culture. Friedrich Nietzsche, Sämtliche Werke: Kritische Studienausgabe, vol. 2, p. 320, eds. Giorgio Colli and Mazzino Montinari, Berlin, de Gruyter (1980). Human, All-Too-Human, "Man Alone With Himself," aphorism 499, "Friend," (1878).
Wordplay between Nietzsche's coinage Mitfreude ("rejoicing in our joy") and Mitleiden ("suffering over our suffering" or, more conventionally, "pitying").)