Imbalances in contractual exchange relationships are a phenomenon that every civil law system has to deal with: an overpowering contractual partner faces a weak one, so there is a risk that the weak contractual partner will be exploited. In such situations, the question arises as to whether and to what extent a legal system wishes to take protective measures for the weaker party. Since the 12th century, Roman and canon law have disagreed on exactly this question, as shown by the legal institution of the laesio enormousis. For some, it was a universal means of comprehensively correcting unfair contractual relationships, while others saw it as a mere exception whose application should be limited. The city and country rights made their own sense of it up until the 17th century. The present work deals with the exciting history of this process of reception.