Reverse normals

In design terms, reverse normals are normals that got reversed, flipped, or inverted and point in the opposite direction. For example, on average, a sphere's normals are pointing outward, making it look like a fuzzy monster or bacteria. When you have its normals reversed, they point inward. Why does it matter?

Flipped normals change the face orientation, showing its backside. As a result, the shading changes too, and light faces look dark, while dark faces turn into light.^[1]