A priest, an engineer and an economist are stranded on a desert island. The first order of business is to get some food. The priest suggests that they all pray. The practical-minded engineer suggests that the three men make a net to catch some fish. But where will they find the necessary materials? The priest and the engineer turn to the economist and ask him if he has any ideas. The economist replies, "Assume a fish."
This well-worn economist joke summarizes one of the chief flaws in contemporary economic theory. That theory almost completely ignores the role of physical resources, assuming they will always be available in the quantities we need at prices we can afford at the time we need them. When those resources aren't available, that theory begrudgingly accepts that there will be some damage to economic activity, but tends to greatly underestimate the impact. This conceptual flaw explains why economists in most financial institutions and governments and thus investors are not especially alarmed at the loss of energy resources as stock market indices remain not too far from their recent highs.
For a good summary of how contemporary economic theory goes off the rails, Australian economist Steve Keen offers a mercifully brief and comprehensible explanation. Here I will relate one critical part of that explanation. About 5.7 percent of U.S. GDP is devoted to procuring and distributing energy. Most economists will tell you that a 10 percent decline in energy availability would have a small effect on the U.S. economy. They would take the percentage of the economy devoted to energy, in this case 5.7 percent, and multiply it by 10 percent to arrive at a 0.57 percent reduction in economic activity.