Flint-knapping

TP has argued, convincingly, that the practice of banging the rocks together to create useful hand-held tools is quite possibly the oldest profession in the human race. This leads to having more things to barter and trade in exchange for other goods and services, as well as giving the more thoughtful human beings an appreciation of what shaped and dressed rocks might be capable of, vis-a-vis piling them stably on top of each other to create a structure capable of keeping wind, rain, and inconvenient sabre-toothed predators, out.