The author searches into the reasons for the perpetuation of inefficient institutions. The monastery of Sta. Maria de Montederramo (Orense, Galicia) in the 13th century lets to underline the existence of formal and informal institutions defining agents' choices whose interests are building up in the process of social interaction. Moreover those interests emerge within socio-cultural context, rather than as the outcome of the institutional constreints over a given nature as profit maximazers. The article reviews the classical debate about the Cister. Given the Rule of the Order it is argued that Cistercians pursued the organization of coherent territorial estates, exclusive property rights over the land and own labour force. Working on the case-study, the gap between the theoretical principle of the Order and the specif management and contractual agreements about land tenancy are considered. The conclusion puts forward that monasteries were devices of accumulation because they developed practices of reciprocity, redistribution and identity within the peasant communities and through the organization of personal and social networks with some of the outstanding members of the local community. In the tied web of social and cultural dynamics, the economic patterns were hammered out.