Boundaries are of critical importance in true 3-D environments

"The universe comes into being when a space is served or taken apart.

The skin of a living organism cuts off an outside from an inside.
So does the circumference of a circle in a plane.

By tracing the way we represent such a severance, we can begin to reconstruct,
with an accuracy and coverage that appear almost uncanny,
the basic forms underlying linguistic, mathematical, physical, and biological science,
and can begin to see how the familiar laws of our own experience follow
inexorably from the original act of severance.

The act is itself already remembered, even if unconsciously,
as our first attempt to distinguish different things in a world where, in the first place,
the boundaries can be drawn anywhere we please."