In Sein und Zeit, Heidegger claims that (1) das Man is an 'existential' i.e. a necessary feature of Dasein's Being; and (2) Dasein need not always exist in the mode of the Man-self, but can also be eigentlich, which I translate as 'self-owningly'. These apparently contradictory statements have prompted a debate between Hubert Dreyfus, who recommends abandoning (2), and Frederick Olafson, who favors jettisoning (1). I offer an interpretation of the structure of Dasein's Being compatible with both (1) and (2), thus resolving the Dreyfus-Olafson debate. Central to this resolution is the distinction between das Man and the Man-self. Das Man is one of three existential 'horizons', or fields of possibilities; the other two horizons are the world and death. At any time, Dasein encounters entities in one of two basic modes: either by 'expressly seizing' possibilities of the horizon, or by occluding these possibilities. These modes are 'existentiell', i.e. features of Dasein's Being that are possible, but not essential. Self-ownership and the Man-self are the two basic existentiell modes of being oneself, i.e. projecting everyday possibilities of oneself appropriated from the horizon of das Man. What differentiates these two modes is the stance one takes to the possibility of death, the existential horizon of being oneself.