I don’t know if this quote is really from Ezra Pound, or whether Jimmie Dale Gilmore has misremembered something else into a wonderful sentence.
Here it is:
The poem fails when it strays too far from the song, and the song fails when it strays too far from the dance.
Gilmore has cited the quote in a number of interviews, including this one.
I guess that’s what poets (and Count Basie!) are for: nailing with extreme brevity what the rest of us take a lot longer to swing at, and usually miss.