In this paper, we present some of the reasons why defining social work is a difficult task. A brief history of the definition of social work is presented. We introduce a division of definitions of social work into the enumerative and abstract. The first fail to cover the entire palette of social work practices, while the second are paradoxically both too narrow and too inclusive. In order to tackle the problem of the over-inclusiveness of the definitions, we delimit the area of operation of social work using the duality of Habermas' lifeworld and system. We maintain that Habermas' theory should be used as a guideline for re-thinking what 'goes wrong' when social work is to be defined. Namely, social work practice mainly takes place in the borderlands between lifeworld and system, where both fail. This fact influences the definitions of social work, its theory, and its practice. The definition of social work is dependent not only on local knowledge and determinants, but on social problems that are local but also globally determined as well. As social problems change and evolve, the definition of social work remains a never-ending story.