You never see an object's color directly — you see light bouncing off it. Value (how light or dark a tone is) is really a record of which way the surface faces the light. Move the one lamp and every tone re-sorts at once.
On a curved form, light lays down a fixed sequence: a small bright highlight, the broad light, the halftone, then the surprise — the darkest band is not the far edge but the core shadow, right where the surface turns away. Just past it, light bounces up off the table as reflected light, so the shadow feels luminous rather than dead.
Rake the lamp to the side and you get the fullest range — that gradation is what turns a flat circle into a sphere. Swing it behind and the form drops into a rim-lit near-silhouette: chiaroscuro, the drama Caravaggio built whole paintings on.
Drop the lamp low and the cast shadow stretches long across the table — that is what anchors the form to the ground. A flat cube face, by contrast, takes one single flat value: same lamp, different form.
Something in the simulation stopped unexpectedly — the lesson continues without it. Nothing you did was wrong; you can move on.