There is growing consensus that the psychiatric disorders defined by the DSM have limited utility in basic research. Specifically, studies aiming to elucidate specific biological, genetic, or cognitive underpinnings of disorder categories appear, at times, far-fetched. In this talk, I will present evidence in favour of a dimensional approach; specifically, one that aims to characterise cognitive processes relating to specific, trans-diagnostic clinical dimensions. Presenting data from a series of large online studies, I aim to demonstrate that these trans-diagnostic psychiatric dimensions, which encapsulate distinct aspects of psychopathology, are dissociable in terms of a range of cognitive processes that were previously confounded in the DSM-based framework. Specifically, I will show that confidence, and its relationship with action, dissociate symptom dimensions of anxious-depression, compulsiveness and social withdrawal. Across several studies, we find that cognitive dysfunctions/enhancements show closer coupling and greater specificity with trans-diagnostic dimensions compared to assessments based on DSM categories. These findings underscore the potential of a dimensional approach, that appreciates the continuum of mental illness, as an avenue towards precision medicine in psychiatry.