Surprisingly Simon’s activities at the Cowles commission remain largely unexplored; while Simon and the Cowles shared a twofold wish to operationalize economics and to formalize human decision making. This is also during his time at the Cowles commission that Simon produces his emblematic paper formalizing bounded rationality. Furthermore, Simon claims that his participation at the Cowles was decisive in his awarding of the Nobel Prize. The aim of the paper is to produce such scrutiny. As such the claim of the paper is that Simon’s relationship with the Cowles commission and its members was a bittersweet one. Indeed, such a collaboration started enthusiastically from both sides and ended surrounded by indifferences. We offer three explanations to this bittersweet relationship. First, both the Cowles and Simon shared a wish to formalize decision making problems; although, they had different conceptions about mathematical tools and the articulation between theory and empirics. Second, the irreconcilability of their conception of optimality threatened their common interest in operational research. Third, and more globally, Simon’s and the Cowles’s research agendas were not stabilized during this period explaining the enthusiastic phase as well as the cold one, once these two research agendas stabilized, but in different directions. The paper distinguishes four periods from 1947 to 1954 during Simon’s time at the Cowles. Each section of the paper deals in turn with one of these four periods.