In this article, the aspect of participatory decision-making in the constitution is considered based on the kind of action and relationship. Accordingly, the research focused on the parties of the second national assembly, which did not proceed towards constructive negotiations even in the first step of decision making (i.e. conflict resolution). Therefore, the “disarmament conflict”, or “Atabak Park” case, was chosen, and the reactions of the parties to the conflicts in each stage were studied. These reactions converted the initial verbal and legal disputes into a military struggle. In this regard, related historical resources based on the stairway model of interests/ rights/ power of Fisher and based on “Fuzzy Analysis method” were read out in the frame of interpretive historical sociology. After coding the historical documents and estimating the membership numbers of the fuzzy-set “agents depend on the highly costly process of conflict resolution”, it was found that the parties gradually used five types of methods, including the highly costly processes of 0.3, 0.6, 0.9, 0.9 and 1. Different major weaknesses in decision-making such as lack of holistic view and adequate information, lack of alternative and fair solutions, and wrongful trust led to this disaster.