One way in which fact finders are supposed to determine the reasonableness of a defendant is via a counterfactual test that personifies the reasonable person. We are to imagine the reasonable person being in the defendant’s circumstances. Then we are to determine whether the reasonable person would have done as the defendant did. This paper argues that, despite its prevalence, the counterfactual test is a hopeless guide to determining defendant reasonability. In brief, the test is of the wrong sort to give fact finders the requisite guidance. What we are after is not a counterfactual judgment (what the reasonable person would do) but instead is a question of possibility (what could the reasonable person do). However, since the only thing impossible of the reasonable person is being unreasonable, personifying the reasonable person cannot offer any useful guidance on this question.