You were doing well until you got to this point. The 'break fall' concept of spreading the impact over a larger (body) surface area works just fine in the real world. Watch some of those parkour (free running) videos on youtube and see how the way they roll on landings allows them to drop from heights that would break bones if they didn't. Or watch some vertical skateboarding and watch how when the skaters bail out of a trick up in the air, they fall ten feet or so and land on their knee which has a plastic cap on it that allows them to slide the rest of the way down the ramp, harmlessly spreading that impact over a long distance and resulting in an impact one barely feels.

Helmets can have these same two components. The shell is supposed to hold the foam together so that the impact is spread out over a bigger distance around the head, and a hard/smooth shell will allow the head to slide upon impact therefore scrubbing off the energy over a larger distance/time.

OK, none of that means I support mandatory helmet laws or believe the helmets on the market that people use are providing a net positive benefit: I don't.