The broad generalization often made about trade is that it can make everybody better off. This economic principle is popularly proclaimed in the introduction to an economics textbook by Mankiw and Taylor, and therefore taught to many, if not all, students attending introductory courses in economics.
Closed cycles can be found in all aspects of life, except in our economy. In nature, the fallen leaves produced from trees nourish the soil with vital minerals which, in turn, serve plants to grow and fruits to form. Natural ecosystems do not produce waste and use all resources as efficiently as possible.