Video narration
Why do a spoon's hollow side and bulging side reflect light so differently? The hollow side curves inward, like a concave mirror; the bulging side curves outward, like a convex mirror. Imagine parallel rays arriving at each. On the hollow curve, they reflect toward a spot in front, where they actually meet. That spot is the focal point: where the rays meet. On the outward curve, they spread apart. Trace them backward, and they seem to come from a focal point behind the mirror, though they never meet there. The curve doesn't change the reflection rule. At each point, light leaves at the same angle it arrived, measured from a line perpendicular to the surface. Change the surface's direction, and you change each ray's path. So the hollow curve brings parallel rays to a real focus; the bulging curve spreads them as if from behind.