Most people believe the vision system exists solely in the eyes.
In reality, the eyes make up only a small part of the system. Think of the eyes like a camera in a TV studio, because, just like that camera, all the eyes do is pick up the image. Most people have never given any thought to how important it is to be able to recognize other people. They just take this task for granted, because for them it is automatic. As you can imagine, the more people in a given place try to look alike, the greater a problem this presents for face blind people.