The story of national judges’ participation in the process of dialogue with the Court of Justice of the European Union (ECJ) pursuant to Article 267 TFEU is a well-known one. There have been many scholarly efforts to explain and theorize the—lack of—participation of national courts in the mechanism. Indeed, various constitutional, institutional, procedural, cultural, political, and individual factors are pointed out to explain this engagement. Yet, it may come as a surprise that still much remains unknown. The available empirical data concerning the potential causes of the national judges’—non—participation is limited to a number of EU member states and is mostly confined to lower courts judges. It is the aim of this Article to partly fill the void in the literature and to provide novel empirical data gained in the course of semi-structured interviews among judges and court référendaires of three Belgian highest courts. The interviews provide insight into the possible factors driving concerned national judges when deciding (not) to refer preliminary questions, including the role and significance of the obligation to refer which is to be found in Article 267 TFEU and the Cilfit-criteria.