The scope of this paper is to introduce and explore the problems concerning the neglect of a diagnosis about how the world really works in the formulation of normative theories – mainly normative theories of judicial decision-making. These are not conceptual or empirical problems, but rather methodological issues. Taking them seriously is crucial for the methodological accuracy of the dialogues between normative legal theories and the explanations provided by other sciences about the behavior of specific agents (like judges). This is a decisive step for the effective relevance of prescriptions based on normative theories in the legal domain.