The phrase, “just enough rope” is a shortening of, “give him/her just enough rope to hang himself/herself.” Giving a person, “just enough rope” in this way means setting them up for failure. In the song, the person being setup for failure
In rhetoric, truncating a commonly known phrase in this manner is called anapodoton.
And using common phrases in this way is something Yorke has a history of doing, as I’ve tried to document.
His father sold chemical-engineering equipment and was a champion university boxer. “One of the first things he ever bought me was a pair of boxing gloves,” says Yorke. “He used to try to teach me to box, but whenever he hit me, I’d fall flat on my ass.” When Yorke was 8, his family moved to Oxford. At 10 he formed his first band, and two years later he wound up at a boys boarding school near Abingdon, England, where he spent several of his most unhappy years. He had few friends, fought frequently and, despite his formative training, usually lost boxing matches.
Colin Greenwood, in an interview with The Word magazine (now defunct, article mirrored here), said Thom Yorke’s “bobbly head thing” while dancing is “a hangover from the days when Thom’s father taught him how to box. ‘Thom’s got really broad shoulders,’ says Colin. ‘When you see them go down, boxer-style, that means he’s really enjoying it.'”
[edit Jan 2, 2021 to correct link to citizeninsane.eu]