|The “garment of Nessus”, as depicted, showing Lichas bringing the garment of Nessus to Hercules, woodcut by Hans Beham, circa 1542-1548.|
Hercules had shot the centaur Nessus with a poisoned arrow for having attempted to rape his wife, Deianeira. As he died, the centaur dipped his robe in his blood and gave it Deianeira. When Hercules abandoned her for Lole, Deianeira sent him the robe as revenge: when he put it on, he was wranked with pain and died, throwing himself onto a burning pyre in order to escape from the torment. 
In a 21 Nov 1827 letter to German polymath Johann Goethe’s friend, German composer Carl Zelter, Goethe explained how his 1809 Elective Affinities, his self-defined best book, had been the Robe or Garment of Nessus to many who read it: 
“Customers, no doubt, sometimes allow the tailor to choose a particular stuff, but they insist upon having the coat fitted to their own bodies, and are highly indignant, if it proves too tight, or too loose; they are most comfortable, when wearing the loose dressing-gowns of the day and hour, in which they can feel as they like; you may perhaps remember, that they treated my Elective Affinities as though it had been the garment of Nessus.”
The phrase also frames the title of Alfred Steer’s 1990 book Goethe’s Elective Affinities: the Robe of Nessus. 
1. Benjamin, Walter. (1921). “Goethe’s Elective Affinities (“Robe of Nessus”, pg. 310; note 9, pg. 358)” (scribd), first published by Hugo von Hofmannsthal in the Neue Deutsche Beitrage (1924/25); in: Selected Writings, Volume 1: 1913-1926 (Elective Affinities, pgs. 297-360). Harvard University Press, 1966.
2. (a) Mahoney, Dennis F. (2004). The Literature of German Romanticism (“As if to the robe of Nessus”, pg. 262). Camden House.
(b) Goethe, Johann and Zelter, Carl F. (1892). Goethe’s Letters to Zelter: with Extracts from those of Zelter to Goethe (Nessus, pg. 307; God, pg. 308). G. Bell and Sons.
3. Steer, Alfred G. (1990). Goethe’s Elective Affinities: the Robe of Nessus (§4: Chemical Conversion, pgs. 37-). C. Winter Universitatsverlag.
● Shirt of Nessus – Wikipedia.