The Weiss affair, culminating in the BVerfG ruling of 5 May 2020 (Weiss II), marks a break-up point in the long-standing dialogue between the BVerfG and the CJEU. The judges in Karlsruhe refused to follow the decision rendered by the CJEU in a preliminary ruling (Weiss I) and ordered EU institutions to provide further clarifications on the proportionality assessment of the Public Sector Purchase Programme. This paper claims that the principles applied by the BVerfG in Weiss I are quite similar to those employed in the Gauweiler and Landeskreditbank-Banking Union cases. Considering that background, it will be argued that the construction of the principles employed by the BVerfG for the judicial review of EU acts did not undergo dramatic changes over time. The different outcome of Weiss II is due to the fact that, according to the BVerfG, insufficient elements of explanation and justification were provided by the ECB and the CJEU. Therefore, the central problem of Weiss II ends up being a procedural question of allegedly insufficient statements of reasons. From Gauweiler to Weiss II, one also sees the development of the standards for the judicial review of the ECB’s decisions, in the fields of both monetary policy and banking supervision.