It is assumed that comparative legal studies, through its deep and historical analysis of law and its dissociation in legal formants, have contributed to understanding the importance of the different factors that shape legal rules. In this article, emphasis is given to a factor that is sometimes neglected in legal narrations: legal mentality or, more simply, the inherent logical way of thinking and its influence in shaping legal rules. The area of investigation is the legal relationship between principal and agent. It is a narration that selects a specific “fil rouge” to link different “pieces” throughout European history to compose a mosaic of different factors that may have contributed to developing a certain legal mentality in this area of law. The legal mentality is nothing more than the product of the extra-legal contexts in which principal and agent operate. In reference to the extra-legal context, it means the importance, above all, of the situations of proximity between the two parties: proximity that could be “spacial” ( i.e. , they are part of the same small community), or “relational” governed by extra-legal forms of belonging to the same group, for instance families (broader or narrower ones) or clans. This narration starts with a glance at the ancient agreement of mandatum and its roots in the Roman idea of “friendship” and personal bond. Then it continues by touching on a source of the medieval companies: the family bond, one of the stronger and more trustworthy relationships at the time. It will be shown that some aspects of that relationship are not dissimilar from the ones later formed by the case law of the English Chancery Court in the field of the law of agency. This could be seen as a result of the legacy of the stratification of a certain legal mentality shaped by a context that was created by extralegal relationships. Nowadays the modern fading of the personal bond between principal and agent has highlighted an important evolution: there was proximity then depersonalization: this is reflected in the evolution of legal rules, for instance, in French, Italian and English national law. Finally, the case of the “real” or “absolute” irrevocability of the authority shows that the agency relationship, constructed in a breeding ground characterized by trust and utilized to protect the principal's interest (or even the principal's interest), could become - through related or linked contracts - an instrument of more complex agreements. In these cases, the interest of the agent or third parties (such as creditors, contractual counterparts or “beneficiaries” in the broad sense) could lead those transactions far from the original idea of mandat or mandato or agency. In those situations, the “causa” of the agency (to use a concept dear to civil law tradition) changes and its roots in personal bond and the principal's interest loses its strength as it is mirrored, once again, in the legal rules.