All disciplines use models. So what is a model? It is a useful abstraction of reality. It is an abstraction because it does not intend to recreate the real world in a one-to-one scale. Rather, it distills the essence of a situation so that it can be readily deployed in other similar situations.
One reason we need models is because we have limited cognitive capacity—you cannot keep track of all the details all the time. Modeling is a way to filter out irrelevance and to focus on what matters. So models are the lens we use to see the world we want to see. And simplicity is the first criterion.
The second criterion is generality. We don’t want to build a new model for every single situation; that would defeat the very purpose of modeling. Rather, we would like our models to have sufficient generality, so that we can apply the same models to different situations with limited modifications.