We all have first impression of someone we just met. But why? Why do we form an opinion about someone without really knowing anything about him or her – aside perhaps from a few remarks or readily observable traits. The answer is related to how your brain allows you to be aware of the world. Your brain is so sensitive in picking up facial traits, even very minor difference in a how a person’s eyes, ears, nose, or mouth are placed in relation to each other make you see him or her as different. In fact, your brain continuously processes incoming sensory information – the sights and sounds of your world. Theses incoming “signals” are compared against a host of “memories” stored in the brain areas called the cortex （大脑皮层）system to determine what these new signals “mean”. If you see someone you know and like at school, your brain says “familiar and safe”. “If you see someone new, it says, “new—potentially threatening”. Then your brain starts to match features of this stranger with other “known” memories. The height, weight, dress, ethnicity, gestures and tone of voice are all matched up. The more unfamiliar the characteristics, the more your brain may say, “This is new. I don’t like this person.” Or else, “I am intrigued.” Or your brain may perceive a new face but familiar clothes, ethnicity, gestures – like your other friends. so your brain says: “I like this person.” But theses preliminary “impressions” can be dead wrong. When we stereotype people, we use a less mature form of thinking (not unlike the immature thinking of a very young child) that makes simplistic and categorical impressions of others. Rather than learn about the depth and breadth of people – their history, interest, values, strengths, and true character – we categorize them as jocks, geeks, or freaks. However, if we resist initial stereotypical impressions, we have a chance to be aware of what a person is truly like. If we spend time with a person, hear about his or her life, hopes, dreams, and become aware of the person’s character, we use a different, more mature style of thinking—and the most complex areas of our cortex, which allow us to be humane.