We aim for rationalizing Enterprise Architecture, supplementing models that express EA designs with models that express the decision making behind the designs. In our previous work we introduced the EA Anamnesis approach for architectural rationalization, and illustrated it with a fictitious case study.In this paper we evaluate our approach in terms of its ability to capture design rationales in the context of a real life case study. Together with stakeholders from the business and IT domains of a Luxembourgish Research and Technology Organization, we captured the design rationales behind the introduction of a new budget forecast business process. Our case study shows that EA Anamnesis can reflect the design rationales of the stakeholders, also linking business and IT concerns. Furthermore our study shows that, for this particular case, the stakeholders often used heuristics (commonsensical “short cuts”) to make their decision, or even made decisions without considering alternative choices. Finally, we discuss what the lessons learned from this case imply for further research.