The main contribution of this paper is twofold. First of all, it focuses on the decisional process that leads to the creation of a social norm. Secondly, it analyses the mechanisms through which subjects conform their behaviour to the norm. In particular, our aim is to study the role and the nature of Normative and Empirical Expectations and their influence on people's decisions. The tool is the Exclusion Game, a sort of 'triple mini-dictator game'. It represents a situation where 3 subjects - players A - have to decide how to allocate a sum S among themselves and a fourth subject - player B - who has no decisional power. The experiment consists of three treatments. In the Baseline Treatment participants are randomly distributed in groups o...