This study aims to carry out reflections towards explaining the paradox of management accounting stability, or, why the implementation level of new accounting techniques and concepts in companies is below the expected. Management accounting theory is strongly oriented by the neoclassical theory of the firm, but neoclassical economics was developed by economists to predict behavior at the industry and market levels. It was not intended as an explanation of the behavior of managers within firms. This paper criticizes neoclassical theory and argues that according the OIE - old institutional economics, management accounting can be seen as institution formed through habits and routines of a social group. The institutional approach enables organizations to reproduce and legitimate behaviors and to achieve organizational cohesion. This work indicates that firms do not implement new concepts from management accounting because these were not institutionalized.