单项选择题

Faces, like fingerprints, are unique. Did you ever wonder how it is possible for us to recognize people Even a skilled writer probably could not describe all the features that make one face different from another. Yet a very young child—or even an animal, such as a pigeon—can learn to recognize faces. We all take this ability for granted.
We also tell people apart by how they behave. When we talk about someone’s personality, we mean the ways in which he or she acts, speaks, thinks and feels that make that individual different from others.
Like the human face, human personality is very complex. But describing someone’s personality in words is somewhat easier than describing his face. If you were asked to describe what a "nice face" looked like, you probably would have a difficult time doing so. But if you were asked to describe a "nice person", you might begin to think about someone who was kind, considerate, friendly, warm, and so forth.
The main idea of this passage is ______.