In Orwell's famous article "Politics and the English Language," he writes:
DYING METAPHORS. A newly invented metaphor assists thought by evoking a visual image, while on the other hand a metaphor which is technically "dead" (e.g. iron resolution) has in effect reverted to being an ordinary word and can generally be used without loss of vividness. But in between these two classes there is a huge dump of worn-out metaphors which have lost all evocative power and are merely used because they save people the trouble of inventing phrases for themselves. Examples are: Ring the changes on, take up the cudgel for, toe the line, ride roughshod over, stand shoulder to shoulder with, play into the hands of, no axe to grind, grist to the mill, fishing in troubled waters, on the order of the day, Achilles' heel, swan song, hotbed. Many of these are used without knowledge of their meaning (what is a "rift," for instance?), and incompatible metaphors are frequently mixed, a sure sign that the writer is not interested in what he is saying.
I believe I do know what a rift is, but I am unsure if I get his meaning here. In the catalogue of worn-out metaphors preceding this question, there is no mention of (and as far as I can see, no allusion to) "rift".
What is his meaning here?