Context: In a letter of consolation to Apollonius on the death of his son, Plutarch urges him not to be excessive in his grief. A short life might be happier and more agreeable than a long one. One who dies young may not experience all the joys in life, but he does not have to endure the sorrows either. And any person knows that men are mortal and must die at some time. The proverb Plutarch attributes to Plato, but it is also ascribed to Pythagoras, Chilo, Thales, Cleobulus, Bias, Solon, Socrates, and to Phemone, a mythical Greek poetess of the ante-Homeric period. According to Juvenal (Satire XI, 27) the precept came from Heaven, Chaucer (The Canterbury Tales, "The Monk's Tale" line 3329) says: "Ful wys is he that can himselven knowe." Cervantes (Don Quixote, Part II, Book IV, chapter 42) says: "Make it thy business to know thyself, which is the most difficult lesson in the world." Plutarch says:
There are two of the inscriptions at Delphi which are most indispensable to living. These are: "Know thyself" and "Avoid extremes," for on these two commandments hang all the rest. These two are in harmony and agreement with each other, and the one seems to be made as clear as possible through the other. For in self-knowledge is included the avoidance of extremes, and in the latter is included self-knowledge.