Reasons-responsiveness theories of moral responsibility are currently among the most popular. Here, I present the fallibility paradox, a novel challenge to these views. The paradox involves an agent who is performing a somewhat demanding psychological task across an extended sequence of trials and who is deeply committed to doing her very best at this task. Her action-issuing psychological processes are outstandingly reliable, so she meets the criterion of being reasons-responsive on every single trial. But she is human after all, so it is inevitable that she will make rare errors. The reasons-responsiveness view, it is claimed, is forced to reach a highly counterintuitive conclusion: she is morally responsible for these rare errors, even though making rare errors is something she is powerless to prevent. I review various replies that a reasons-responsiveness theorist might offer, arguing that none of these replies adequately addresses the challenge.