A 1976 paper argued that past economic data can't predict a new policy's effects

Robert Lucas argued that traditional economic models, built from historical relationships between things like spending and employment, break down the moment policy actually changes — because people adjust their expectations and behavior in response to the new rules, not just the old data. The Lucas critique reshaped macroeconomics around modeling how rational people react to policy itself.

— Robert Lucas Jr., Econometric Policy Evaluation: A Critique — 1976