In complex systems cause and effect are often not closely related in e — Jay Wright Forrester

"In spite of the tentative nature of the world model described here, various conclusions are drawn from it. Man acts at all times on the models he has available. Mental images are models. We are now using those mental models as a basis for action. Anyone who proposes a policy, law, or course of action is doing so on the basis of the model in which he, at that time, has the greatest confidence. Having defined with care the model contained herein, and having examined its dynamic behavior and implications, I have greater confidence in this world system model than in others that I now have available. Therefore, this is the model I should use for recommending actions. Those others who find this model more persuasive than the one they are now using presumably will wish to employ it until a better model becomes available."

"In concept a feedback system is a closed system. Its dynamic behavior arises within its internal structure. Any action which is essential to the behavior of the mode being investigated must be included inside the system boundary."

"[The engineer] must identify the significant and critical problems, but in his education, problems have been predetermined and assigned. He must develop the judgment to know what solutions to problems are possible, but in school the problems encountered are known to have answers. He should be excited by new and unsolved challenges, but for 20 years he has lived in an educational system where he knows he is repeating the work of last years students."

"Formulating a model of a system should start from the question “Where is the boundary, that encompasses the smallest number of components, within which the dynamic behavior under study is generated?”"

"The strongest criticism has come from some economists. The objections range from simple misunderstanding, through belief that essential structures have been omitted from the world model, to concern over the costs and feasibility of halting economic growth. Although there is a basis for the criticisms, they have not had sufficient substance to dismiss the central issues. The debate seems to be gradually moving away from the question of whether or not industrial growth must slow to the question of what strategy should be used to limit growth. The latter question, however, remains unanswered."

"It seems traditional for explicit models of social systems to be greeted by vague criticisms about their lack of perfection. Instead, we need equally explicit alternatives with a demonstration that the alternative leads to a different and more plausible set of conclusions. By proposal and counter proposition our understanding of social systems can advance."