Constitution-making should not, in theory, result in an absolute no-win situation. But Chile’s Constitutional Process of 2019-2022 is an example of it. To place the Chilean Constitutional Process in a comparative and historical perspective, out of the 179 plebiscites on new constitutional processes that that have been held around the world between 1789 and 2016, only 6% of these have rejected a newly drafted constitution. The failure of Chile’s Constitutional Process was as historic as the opportunity to write a new constitution under the conditions that the Chilean Constitutional Convention drafted it: with gender parity, high inclusion of Independent citizen-legislators, regional representation, and a proportional Indigenous peoples’ quota. What went wrong? A series of explanations and autopsy reports have been offered but these fail to explicitly identify the feature that, I argue, was essential to determine the success or failure of the Process: its procedural architecture. This paper will argue that procedures significantly and negatively affected decision-making processes in the Constitutional Convention and can be considered one of the main causes of the failure of the Constitutional Process. The Chilean Constitutional Process failed greatly due to both, procedures that were externally developed and imposed on the Constitutional Convention and procedures that were internally developed and adopted by the Convention. The exogenously and endogenously designed procedural architecture that bound the Convention hindered effective decision-making processes and the investigation analyzes some of the most impactful procedures in the Process connected to decision-making in constitution-making. The argument advanced in this investigation evaluates the impact of these procedural features on the decision-making processes and dynamics of the Constitutional Convention from a political epistemology perspective. With a multi-methods approach using qualitative and quantitative data, this paper analyzes how procedures were developed in the Constitutional Process, the values and limitations of these procedures, and the impact of these procedures on the dynamics of the Constitutional Convention.