"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."

“No plea about inadequacy of our understanding of the decision-making processes can excuse us from estimating decision making criteria. To omit a decision point is to deny its presence – a mistake of far greater magnitude than any errors in our best estimate of the process.”

“Pestel was a very forceful person and quickly saw the power of system dynamics.”

“The enterprise engineer must be a leader, a designer, and a synthesizer. He is a doer. He understands theory as a guide to practice. He must concern himself with human organization because the pace and success of technology are becoming more dependent on interaction with the social system and less on scientific discovery. In private as well as public research and development, such men must find ways to reverse the deterioration of ethics and efficiency. They will strengthen the information links between physical design and the public so that technology can better serve society. In the public sector they must show the level of wisdom and leadership that can co-ordinate great engineering projects with politics. They will recognise that informing the public and becoming a nucleus for crystallising public opinion is even more important in many programmes than is the underlying science.”

“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 year's students.”

“In complex systems cause and effect are often not closely related in either time or space. The structure of a complex system is not a simple feedback loop where one system state dominates the behavior. The complex system has a multiplicity of interacting feedback loops. Its internal rates of flow are controlled by nonlinear relationships. The complex system is of high order, meaning that there are many system states . It usually contains positive-feedback loops describing growth processes as well as negative, goal-seeking loops. In the complex system the cause of a difficulty may lie far back in time from the symptoms, or in a completely different and remote part of the system. In fact, causes are usually found, not in prior events, but in the structure and policies of the system.”

“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?”