The shadow gives an ordinary object a shape that light alone cannot explain.

Shadow is where an object stops being a flat fact. Light shows the surface; the shadow gives depth, position, time of day and some sense of what the thing would feel like to hold, none of which brightness alone can supply. Absence of light is doing real descriptive work. What is unlit is often what makes the rest legible.

When you next look closely at anything, a cup, a face, a building, spend a moment on where the dark falls. The same holds with people: what somebody leaves out can describe them as accurately as what they show.