[paulddraper]

Image the economy is a field of wheat.

Someone comes in with a tractor plough and plants twice a much wheat as last year. There is now lots of food in the economy and bread and pies.

In fact, the tractor plough plants so much wheat year after year that a few of the farmers stop planting and start working on building and maintaining tractors.

Eventually the tractors do well enough and wheat is cheap enough that the some farmers can afford to raise wheat-fed cattle.