This chapter started from a fundamental question regarding psychopathology: what maintains psychological illnesses. A well-known and shared view is that it depends on faulty reasoning. However, thanks to a wide number of experiments, we demonstrate that patients reasoning is not at all impaired and that they can even reason better than healthy people, but only when they reason on topics relevant to their disturbance. From these empirical observations, we argued that they are motivated to reason effortfully to pursue their goals, e.g., to avoid the harm relevant for their disturbance, thus reducing the likelihood of crucial errors. This view helps us to better understand how a relevant psychological process, such as reasoning, actually works also in healthy people. We argue that it is a tool at the service of our goals. According to a functional and pragmatic account of reasoning, we understood that the best kind of thinking is indeed whatever kind of thinking that best helps people to achieve or protect their goals and reduce the costs of crucial errors, also thanks to emotions, and this is valid for both normal and abnormal people.