Some lessons to be learned from the shale oil or fracking experience are: a) People respond to incentives. b) Human ingenuity keeps postponing the exhaustion of natural resources. c) Predictions of doomsayer experts, like Malthus and Nobel laureate in economics Krugman, should be taken with a grain of salt (caution). d) The Stone Age came to an end, and it was not because of a deficit of stones. Fossil fuels may experience a similar fate. e) All of the above