If we had to stop and reflect on all that we do, there would be too much to think about; we would be totally preoccupied with the small details of everyday life. As impressive as the brain is, there are limits to the amount of information it can process. Routines free the mind from the job of experience and allow us to think of other things.
Habitual patterns are not only characteristic of behavior, but of thought, of knowledge, and of experience in general. The routines we inherit are methods for taking the novelty out of experience, transforming what was originally new and unique into a world so familiar it doesn’t need to come to our attention.
We have categories (fiction, alive, young, important, edible) only for what is in some way relevant. Their relation to us, their relevance, indicates why we are interested in certain things and not others. The space technician has a different set of categories than the dietitian. The criminal and the law enforcement officer operate with the same categories, but their relationships to them — the reason a crowbar, unlocked car or murder weapon is of interest and importance — are quite different.
Categories are flexible, varying with the situation. We expand or alter their importance to fit the circumstances. If you have to seat twenty people for an informal gathering, the category "chair" can include bar stool, piano bench, and pillow. If you need ten chairs for a formal sit-down dinner, pillows are out. Categories recall past situations, transfer knowledge to the present, and tell us what to expect in the future.
Suppose I’m in the market for a new house. I already know much about houses — their common features, their usual problems. Houses have bathrooms and kitchens, plumbing and wiring, backyards and leaky roofs. Before I see it I’m assuming this will be a typical house, and I have a set of expectations that are empty of specific content. It will have a particular color, one or two floors, at least one door, perhaps a basement, an attic, a garage.
When I arrive, I begin to fill in the abstract categories with concrete details. Suppose I discover, after exploring the first floor, that there’s no access to the second floor — lots of second floor windows, but no exterior door and no internal stairway. What kind of house is this? Surely this is not typical, this experience not routine. It presents a situation for which my knowledge is inadequate.
There are many ways we can respond when we encounter something like this. Basically, we can either make the new information conform to what we already know, or we can change the way we’ve been structuring our categories. In this case, either I’ll have to determine that this is not a house at all (perhaps it was originally built as a movie set), or I’ll have to change my idea of what a house is (perhaps some houses are built to look impressively but deceptively large).
This house is admittedly an unusual example, but it is in just such situations, equally simple and mundane, that we learn something new, revise our expectations, and expand our knowledge. It is in situations such as this that the world evolves. And although we usually don’t think of ourselves as restructuring or altering reality, it is just this activity, over the course of a lifetime, that accounts for who we are at any particular moment. It is precisely this activity, over the course of millennia, that accounts for the evolution of our species and the difference between the stone age, the dark age, the industrial age, and what will be called the "modern" age tomorrow. We play the only active role in this process. And to play an active role passively is resignation. This does not have to be the case.