Although Leontief was and still is one of the most recognized names in economics, inextricably linked to the development of input-output techniques, he remained fiercely critical of other economists' works and of the state of economic science during his whole life. To understand his bitterness, we go back to the root of the split between Leontief and the rest of the economics profession, through an examination of the debates that took place in the late 1940s. From his input-output model, conceived as an operational theory of economic interdependencies, Leontief drew a specific approach to economic policy and planning which had a lot of success with government agencies, explaining how he could durably sustain his split from the profession.