Someone in another UX community I participate in shared this idea with is: What if we stop thinking of them as "users" and start thinking of them as stakeholders? What are the consequences for stakeholders if our design, or our experience, fails?
That is, I think, the key element that is missing in most user stories: We assume success. We concentrate on the happy path and don't give a lot of thought to what happens if someone can't ask us their question or can't find out if the product she wants to buy is the right size?
I think the failure of most user stories to take empathy into account is a direct result of the fact that Agile was originally a hardware development process. It's focused on implementation not on the people who will use what's being built.