Ah, that explains why I keep being asked to split a complex feature into pointless pieces that don’t stand alone. No wonder we need so many team hours in sprint planning, to keep track of them all.
No system is perfect for sure. It's a rule of thumb. If it doesn't fit then stick with the really large story that simply cannot be broken down into manageable chunks but it should be a super rare corner case that some piece of work is so huge yet atomically consistent that there is absolutely no human way to break it down, at all, in any way shape or form.