I think this separation is a basic strategy for thinking about a complex world, and probably an effective one. I don't think it's meant to be taken too literally, as if the world were actually like that, although I suppose some do take it that way. I doubt people can generally manage a holistic view of everything, practically speaking. I doubt people can manage very accurate views outside narrow domains. The holistic view is valuable, I just don't think it can be applied fulltime. Compartmentalized and simplified models are valuable too. Maybe necessary.