May not an ass know when the cart draws the horse?
– William Shakespeare
King Lear, Act 1, Scene 4. The Fool says that even an idiot could see it is not the normal order of things when Goneril can boss Lear around. It is a case of the cart leading the horse, he says. Metaphorically Lear and Goreril are a horse and cart, whose roles have been reversed.