" drop the economist’s beloved notion of ‘externalities’, those incidental effects felt by people who were not involved in the transactions that produced them—such as toxic effluent that affects communities living downstream of a river-polluting factory, or the exhaust fumes inhaled by cyclists biking through city traffic. Such negative externalities, remarks the ecological economist Herman Daly, are those things that ‘we classify as “external” costs for no better reason than because we have made no provision for them in our economic theories’.21 The systems dynamics expert John Sterman concurs. ‘There are no side effects—just effects,’ he says, pointing out that the very notion of side effects is just ‘a sign that the boundaries of our mental models are too narrow, our time horizons too short’. "

― Kate Raworth , Doughnut Economics: Seven Ways to Think Like a 21st-Century Economist