Here's a social characteristic that divides us that I think few people are aware of: how often, during a typical face-to-face conversation, do you pay attention to or visualize what your facial expressions must look like to the other person? I first became aware of this distinction during a conversation with friends, where we stumbled on the realization that we are very different from each other in this way. I am almost never aware of my face, whereas one of my friends is aware of it most of...