How does doubt come about? What are the mechanisms responsible for our inclinations to reassess propositions and collect further evidence to support or reject them? In this paper, I approach this question by focusing on what might be considered a distorting mirror of unreasonable doubt, namely the pathological doubt of patients with obsessive-compulsive disorder (OCD). Individuals with OCD exhibit a form of persistent doubting, indecisiveness, and over-cautiousness at pathological levels (Rasmussen and Eisen, 1992; Reed, 1985; Tolin et al., 2003). I (...) argue that the failure in OCD is of an affective nature, involving both excessive epistemic anxiety and hyperactive feelings of uncertainty. I further argue that our adaptive disposition to inquire about the right matters - that is, about propositions which are both epistemically risky and imply harmful possibilities - might depend on these affective mechanisms. (shrink)