People living in developed nations have become disconnected from the everyday processes of civilization that support them. Individually, we are astoundingly ignorant of even the basics of the production of food, shelter, clothes, medicine, materials, or vital substances.

The most profound problem facing survivors is that human knowledge is collective, distributed across the population. No one individual knows enough to keep the vital processes of society going. Even if a skilled technician from a steel foundry survived, he would only know the details of his job, not the subsets of knowledge possessed by other workers at the foundry that are vital for keeping it running—let alone how to mine iron ore or provide electricity to keep the plant operating.

Medicine and surgery, more than many other areas covered in this book, rely heavily on implicit or tacit knowledge—something you have learned how to do but would find extremely difficult to successfully convey to someone else in just words or pictures. In Britain, it takes up to a decade of medical school and on-the-job learning in a hospital to achieve competency as a registrar doctor (the equivalent of a US fellow in a subspecialty), all of this with training and hands-on demonstrations provided by someone already proficient. If this cycle of knowledge transfer breaks with the collapse of civilization, it will be impossible to teach yourself the necessary practical skills and interpretative expertise from textbooks alone.

Food, clothes, medicines, machinery, and other technology inexorably decompose, decay, deteriorate, and degrade over time. ... With the collapse of civilization and the sudden arrest of key processes—gathering raw materials, refining and manufacturing, transportation and distribution—the hourglass is inverted and the sand steadily drains away.