"In the Iliad, the epithets most commonly associated with Achilles among his companions are 'shining, godlike' and 'swift-footed'; the epithet used by Thetis, however, is minunthádios — 'lasting but a short time, of persons, short-lived.' 'Why did I raise you? . . . since indeed your lifetime is to be short, of no length'; 'Now give honour to my son short-lived beyond all other / mortals.'
To this inexorable, not-to-be-prayed-away fact, Thetis obsessively again and again returns. She can negotiate with Zeus for her son’s honor, but not for his life. For the immortal mother, her son’s fame, his prowess, his legendary feats count for nothing in the face of the fact that she knows that she will endure to see him die; an immortal goddess, she knows her grief will be everlasting. The keening of Thetis is one of the most consistent themes in the Iliad. She first appears as if shrouded in a mist of tears and at every appearance thereafter seems to be prostrate, paralyzed with grief for the event that she knows must come."
- Caroline Alexander, from The War That Killed Achilles: The True Story of Homer's Iliad and the Trojan War, 2010.