Because you spend all day staring at a screen

All your work is done with a two-dimensional sheet of glowing glass about 15 inches across.

You do not manipulate the world, except to tap 100 or so half-inch plastic squares and stroke a 5-inch plastic pad.

You do not move through the world, only through the evolving landscapes of light on the screen.

You do not meet people, only their representations on the screen.

Meanwhile, just beyond the edges of that two-dimensional sheet of glowing glass, is the three-dimensional world, where eight billion people throng.