Ironically, just when macroeconomists had begun applying classical and
modern control theory in the late 1970’s, control theorists and applied mathematicians
began to construct new methods to repair adverse outcomes they had
experienced from applying classical and modern control theory to a variety of
engineering and physical problems. They thought that model misspecification
explained why outcomes were sometimes much worse than predicted and therefore
sought controls and estimators that acknowledged model misspecification.
That is how robust control and estimation theory came into being.