This paper warns of two threats to moral responsibility that arise when accounting for omissions, given some plausible assumptions about how abilities are related to responsibility. The first problem threatens the legitimacy of our being responsible by expanding the preexisting tension that luck famously raises for moral responsibility. The second threat to moral responsibility challenges the legitimacy of our practices of holding responsible. Holding others responsible for their omissions requires us to bridge an epistemic gap that does not arise when (...) holding others responsible for their actions—one that we might often fail to cross. (shrink)