This is the section just after the introduction. I've edited the introduction slightly (added a few paragraphs of clarification), but it's still basically the same. The section here deals with the question of how we perceive (detect) depth in our environment:

Human beings generally do not know everything about the environments they inhabit. We also frequently don't have the time or resources required to investigate our environments exhaustively. So it is common for us to be in an environment where we do not understand everything about the environment.

Further, though the human brain is extremely powerful, it has a fairly limited focus. We can keep approximately 7 things “in mind” at the same time1, but we have difficulty handling even two unfamiliar or learning tasks simultaneously. With practise, we can learn to handle a task with less of our attention, but that generally requires learning the patterns quite well. We are also limited in our physical capabilities; we cannot see behind us readily, nor can we normally see around most corners without shifting our position. So, from a practical standpoint, perfect knowledge of our environment is difficult to obtain.

As a result, we are very good at picking out patterns from complex environments and prioritizing our focus on that within the environment which we perceive to be the most critical item. Recall our example of sitting in a cafe from the last chapter. By learning the higher-level patterns of “a crowd” and “traffic”, we can largely ignore that which conforms to the patterns, while picking out more relevant items that do not conform to those patterns.

In a more natural setting, those who live in a jungle learn the patterns of sounds, smells and sights that constitute “the jungle”, and can pick out from those experiences the occasional sounds or sights of a tiger stalking them, or of a predatory snake draped over the limb of a tree. The pattern may only be something slightly off, a silence of birds as the tiger passes, a slightly-too-symmetrical vine, a set of eyes beneath a leaf caught out of the corner of one's eye. Yet it is those patterns, rather than the riot of colour, sound and light that the experience woods-woman will pick out.2

We've used a fairly primitive example here to illustrate the next point. Whether or not an individual has lived in a natural environment, most humans fear environments that they do not understand. It is difficult to say where the fear of the unknown comes from. It may be an instinctual response, created by millions of years of hidden predators killing those who didn't fear the unknown, or it may be learned anew by every generation. Regardless of where the apprehension comes from, most human beings cannot be comfortable in the presence of an unknown.

We fear the unknown.

Combined with an imperfect knowledge of our environment, our fear of the unknown prompts us to take some action to reduce our fear. Commonly learned actions are investigation, intimidation, and avoidance. Individuals can have very different responses to the same unknown environment.

These strategies are refined by the individual according to experience. For instance, if an unknown sound is that of laughter from members of the opposite sex, many individuals will have learned to investigate such an unknown by walking into the unknown situation. The number of individuals who will investigate the sound of gunshots similarly is probably lower and dropping all the time.

The examples so far have been mostly crude, life-or-death situations. For designers the more interesting aspect of our relationship to the unknown is in the more subtle, longer-term “off” signs that humans detect and fear. Society has formed many explanations for the unknown, from religious mythologies through particle physics. Seeing a problem with our current understanding of how the world works, we investigate or create, to try to find a better model that can eliminate the dark corners.

On a societal level, strategies for dealing with the unknown can have a cumulative effect. Those who investigate the unknown and communicate their findings with their society can reduce the total “unknown” space in the world. A systemic organization of this knowledge can let members of the society prosper due to their ability to predict the effect of their actions.

During the late renaissance period in Europe, it was believed that human beings were coming close to understanding everything there was to know about the world. Projects such as “The Encyclopedia” were started with the intention of collecting all knowledge. A human was considered complete only if they understood all of the arts and sciences. Humans saw themselves as living in a bright age when all could be known, all could be mastered, and there was no limit on growth and potential. There would be no dark corners left to hide demons.

Since then, humans have continued to learn. Philosophers such as Hume have seriously called into question whether we can really know anything about our world. Scientists have discovered that the underlying patterns of the world, far from being the simple equations of Newton, are so alien to our understanding that few if any humans can have even a loose intuitive grasp of their operation. Fields of knowledge have multiplied so that, far from any individual being able to master all of human knowledge. It would be nearly impossible even to keep up with the day-to-day production of knowledge. There is far more information than our brief life-spans will encompass. We have mastered the majority of our environments to such an extent that we are the demons waiting in the shadows to consume our society. Most of our unknown situations are now man-made, either physical or social, and most of our fear of the unknown is directed at other humans.

The same mechanisms that allow us to live in a forest are now being brought to bear in allowing us to cope with these new realities. We can learn the patterns of a city as readily as those of a city. We pick out that which doesn't match our model of our environment and focus our attention on it, allowing us to learn and grow. We investigate that which doesn't make sense. We prioritise our investigations according to what seems most important and unresolved.