Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.
— Charles Goodhart, “Monetary Relationships: A View from Threadneedle Street” (1975)
…the features which lead to success in short-term forecasting are unrelated to quantitative policy evaluation, … the major econometric models are (well) designed to perform the former task only, and … simulations using these models can, in principle, provide no useful information as to the actual consequences of alternative economic policies.
— Robert E. Lucas, “Econometric Policy Evaluation: A Critique” (1976)
At the instant of the determination of its position — i.e., the instant at which the light quantum is diffracted by the electron — the electron discontinuously changes its impulse. That change will be more pronounced, the smaller the wavelength of the light used, i.e., the more precise the position determination is to be. … That is, the more precisely the position is determined, the more imprecisely will the impulse be known, and vice-versa.
— Werner Heisenberg, “The Actual Content of Quantum Theoretical Kinematics and Mechanics” (1927) [translated from the German]