This is not to say that the circular flow diagram isn't useful in understanding the basics of an economy, such as leakages and injections. However, it cannot be ignored that the economy intrinsically requires natural resources and the creation of waste that must be absorbed in some manner. The economy can only continue churning if it has matter and energy to power it and the ability to absorb the waste it creates. This matter and low entropy energy and the ability to absorb waste exists in a finite amount, and thus there is a finite amount of inputs to the flow and outputs of the flow that the environment can handle, implying there is a sustainable limit to motion, and therefore growth, of the economy.