Stare the center of the mountain and you'll see a devil's face.
Repeat: Stare and you'll see a devil's face. ...
In 3D graphics, the shading is just as important as the initial design (without shading), and it can be done by using projections relative to a certain light source and stretching the idea of gradient on the surface that may not be smooth at all. Without it, your effort for designing interesting terrains may be wasted.
The picture on the right illustrates before shading while the main picture above (without the moon) shows after: The shading not only makes the picture look more three-dimensional and the wrinkles of the surface surface dramatically but also distorts the perfect symmetry of the object with respect to the center vertical line.
Many say that a typical supermodel's face is wrinkle-free and symmetric; it might explain why people prefer to date in dimly lit lounges instead of sunny outdoors.