“The human brain works by identifying patterns. It uses information from the past to understand what is happening in the present and to anticipate the future. This strategy works elegantly in most situations. But we inevitably see patterns where they don’t exist. In other words, we are slow to recognize exceptions. There is also the peer-pressure factor. All of us have been in situations that looked ominous, and they almost always turn out to be innocuous. If we behave otherwise, we risk social embarrassment by overreacting. So we err on the side of underreacting.”