Lewis M. Dabney has the backstory:
He continually received letters from people he didn’t know, often requests for assistance, and usually having no secretary, he devised the engraved card “Edmund Wilson Regrets That It Is Impossible For Him To,” with a list of twenty-one items from “Read Manuscripts” to “Supply Opinions on Literary or Other Subjects.” It would be sent off with a check beside the line applicable. This card strengthened the impression of a difficult, irascible man made by his battle with Nabokov and by polemics against the IRS and the Modern Language Association. Yet Wilson did most of the things on this list for purposes he approved….”
(Image via About Last Night.)
UPDATE: Here’s a slightly different version of the card. It’s not clear to me which version came first.