The difference between the real world and narrativium is not that in the former people make decisions and things happen for rational, believable, predictable reasons and in the latter they don't. That's the difference between good narrativium and bad narrativium.

The difference between the real world and narrativium is that in the real world things happen in a variety of complex and interconnected ways without necessarily being goal driven. However in a story, HpMoR included, things happen to drive the story along. The author has designed the events of the story to reach his desired end state. That is, in fiction the ending causes the beginning whereas in real life the beginning causes the ending.

Real life doesn't have a narrative. Fiction, rationalist fiction included, does.