Even though the two of them have the same need to own horses, the reason they think this way is as different as their reasons for packing the kids off to Exile Farm. It seems to me that Elly has in in her head that there's some sort of government agency around that holds a test to prove that a person is a responsible adult; the same need to blindly follow a rote housework schedule and to mindlessly panic when packing for a trip seems to inspire the belief that there's only one way to think about the world. There is a voice in her head that tells her that no one actually comes up and says that you're officially grown up but she can will herself to ignore it so that she doesn't have to admit that she's wasting her life for nothing.
John, on the other hand, doesn't have that nagging little voice that alerts him that he's acting like a swinish clod; his arid, bolted-down brain is too rigid to question the lunatic misapprehensions, childish question-begging and self-centered rubber stamp "opinions" that coagulated around his fragile ego so the existence of a concept that doesn't fit inside the file folders in his skull doesn't elicit the human response of asking what he believes and why he believes it. What always happens is that rage and alarm run away with him because the child is trying to trick him into admitting that what he knows to be so isn't.