Our fate moves invisibly! A mystery

Via TF, quoting Grief Lessons: Four Plays by Euripides  by Anne Carson:

Come here, let me share a bit of wisdom with you. Have you given much thought to our mortal condition? Probably not. Why would you? Well, listen. All mortals owe a debt to death. There's no one alive who can say if he will be tomorrow. Our fate moves invisibly! A mystery. No one can teach it, no one can grasp it. Accept this! Cheer up! Have a drink! But don't forget Aphrodite--that's one sweet goddess. You can let the rest go. Am I making sense? I think so. How about a drink. Put on a garland. I'm sure the happy splash of wine will cure your mood. We're all mortal you know. Think mortal. Because my theory is, there's no such thing as life, it's just catastrophe.

TF doesn't say so, but that turns out to be from Alcestis. Here's another version:

Know the nature of human life? Don't think you do. You couldn't. Listen to me. All mortals must die. Isn't one who knows if he'll be alive to-morrow morning. Who knows where Fortune will lead? Nobody can teach it. Nobody learn it by rules. So, rejoice in what you hear, and learn from me! Count each day as it comes as Life-and leave the rest to Fortune. Above all, honour the Love Goddess, sweetest of all the Gods to mortal men, a kindly goddess! Put all the rest aside. Trust in what I say, if you think I speak truth-as I believe. Get rid of this gloom, rise superior to Fortune. Crown yourself with flowers and drink with me, won't you? I know the regular clink of the wine-cup will row you from darkness and gloom to another haven. Mortals should think mortal thoughts. To all solemn and frowning men, life I say is not life, but a disaster.

The context of this is strange: Herakles, newly a guest of Admetus, is drunk and speaking reprovingly to a sad-faced servant; the servant is sad because Alcestis, Admetus's wife, has recently died, a fact that Admetus has concealed from Herakles in order not to drive him away, which would, Admetus belives, reflect badly on the honour and hospitality of his house. To make it even weirder, Alcestis has died in place of Admetus, in a bargain brokered by Apollo; and Pheres, Admetus's father, has just had a bitter argument with Admetus over who should have died (anyone could have, but only Alcestis volunteered).

To continue with the play... Admetus, though overcome with grief, neglects the obvious: that she is dying for him; and he doesn't have to accept her sacrifice. The Chorus appears to subtly mock him; interspersed with his cries of grief, we get such as "Courage! You are not the first to lose... A wife; Different men Fate crushes with different blows" and "Grief has fallen upon you In the midst of a happy life Untouched by misfortune. But your life and your spirit are safe. She is dead, She has left your love. Is this so new? Ere now many men Death has severed from wives." Ah, but then he does get the obvious: Those who hate me will say: 'See how he lives in shame, the man who dared not die, the coward who gave his wife to Hades in his stead! Is that a man? He hates his parents, yet he himself refused to die!'

It all ends happily though. Herakles, appraised by the sad-faced servant of the truth, resolves to defeat Death and restore Alcestis; this he does - Admetus, seeing her back, wisely asks Beware! May it not be some phantom from the Underworld? aware of the Wife of Ushers Well and similar; but it is her entire.