highly connected nodes
Here is an excerpt from "The Origin of Wealth" (Eric D. Beinhocker):
Jain and Krishna created a simulation of an evolving ecosystem of computer creatures. The researchers found that if they randomly removed a "species" from their simulated ecosystem, typically not much happened. Yet, once in a while, removing a random species would set off a cascade of events leading to a mass extinction. Certain species are very densely connected to other species in the web of food relationships and niche competition. Biologists call these keystone species. For example, one might imagine a species of amoeba that was a source of food for various insects and filter-feeding worms, which in turn were food for a variety of birds and mammals, which in turn also had an impact on various plant species, and so on. A sudden drop in the amoeba population at the bottom of this food chain could radiate widely throughout the ecosystem.
The production of cars and personal computers feed an extremely large network of businesses. Hence these consumer goods can be regarded as "keystone species" in the economy. For example, a drop in the aggregate demand for cars will lead to a cascade of negative effects down the extremely complicated supply chain. There will also be secondary effects as the affected firms cut back on investment and personnel.
As the percentage share of keystone consumer products increases in the GDP, economy becomes more sensitive to aggregate demand shocks. The experience (or the fear) of economic distress causes people to cut back on all unnecessary expenditure. The first victims are usually durable goods such as cars and PCs. (By definition, durable goods are things that can be repaired and used for extended periods of time.) When these densely connected industries start to suffer, the economic crisis spreads and deepens very quickly. Conversely, when these industries pick up, their contribution to economic growth is unintuitionally positive.
Consumption patterns will change as civilization advances and new technologies are developed. However our basic needs (e.g. food, shelter, health) will stay the same, and economic contractions (and expansions) will continue to be amplified by the densities introduced into the economy's network topology by the complex-but-non-essential goods.