Tadeusz Kotarbinski's 120th anniversary of birth gives an opportunity to remind his extraordinary personality and the philosophy of 'efficient activity' published in 1955. Despite the criticism of his philosophy by Marxist scientists, T. Kotarbinski managed to initiate the development of research on scientific organisation and management in the Polish Academy of Sciences Praxiology Institute. The author - a latter leader of the unit and T. Kotarbinski's collaborator insists that his philosophical concepts are live issues and need to be propagated nowadays.