The fact that most resources can provide a variety of different services is of great importance for the productive opportunity of a firm. It is the heterogeneity, and not the homogeneity, of the productive services available or potentially available from its resources that gives each firm its unique character. Not only can the personnel of a firm render a heterogeneous variety of unique services, but also the material resources of the firm can be used in different ways, which means that they can provide different kinds of services. This kind of heterogeneity in the services available from the material resources with which a firm works permits the same resources to be used in different ways and for different purposes if the people who work with them get different ideas about how they can be used. In other words there is an interaction between the two kinds of resources of a firm-its personnel and material resources-which affects the productive services available from each.