A common practice in research on unconscious cognition is to exclude trials with high visibility ratings or to exclude participants with high sensitivity for the critical stimulus. Based on standard signal detection theory for discrimination judgments, we show that post-hoc trial selection only isolates points of neutral response bias but remains consistent with uncomfortably high levels of sensitivity. We argue that post-hoc selection constitutes a sampling fallacy that capitalizes on chance, generates regression artifacts, and wrongly ascribes unconscious processing to stimulus conditions that are far from indiscriminable. As an alternative, we advocate the study of functional dissociations, where direct (D) and indirect (I) measures are conceptualized as spanning up a two-dimensional D-I space and where single, sensitivity, and double dissociations appear as distinct curve patterns. While most studies employing post-hoc selection are confined to only a single line of that space where D ≈ 0, functional dissociations can utilize the entire space, circumventing requirements like null visibility and exhaustive reliability, and allowing for the planful measurement of theoretically meaningful functional relationships between experimentally controlled variables.