Modelling is an essential and insperable part of all scientific, and indeed all intellectual, activity. How then can we treat it as a separate discipline? The answer is that the professional modeller brings special skills and techniques to bear in order to produce results that are insightful, reliable and useful. Many of these techniques can be taught formally, such as sophisticated statistical methods, computer simulation, system identification, and sensitivity analysis. There are valuable tools, but they are not as important as the ability to understand the underlying dynamics of a complex system well enough to access whether the assumptions of a model are correct and complete. Above all, the successful modeller must be able to recognise whether a model reflects reality, and to identify and deal with divergences between theory and data.

William Silvert, "Modelling as a discipline"