Analyzing argumentation semantics with respect to the notion of skepticism is an important issue for developing general and well-founded comparisons among existing approaches. In this paper, we show that the notion of skepticism plays also a significant role in order to better understand the behavior of a specific semantics in different situations. Building on an articulated classification of argument justification states into seven distinct classes and on the definition of a weak and a strong version of skepticism relation, we define the property of skepticism adequacy of an argumentation semantics, which basically consists in requiring a lesser commitment when transforming a unidirectional attack into a mutual one. We then verify the skepticism adequacy of some literature proposals and obtain the rather surprising result that some semantics fail to satisfy this basic property.