Model model, a simplified picture of how something works or what it is like, helps us think about the world without carrying all of it in our heads. A map is a model of a place. A recipe is a model of a dish. A story can be a model of how people behave. We use the model to predict, to plan, or to explain. The model is not the thing itself. It is a stand-in that captures some relations and leaves others out. First, we notice patterns in the world. Then we make a simplified version—in words, in drawings, in objects. Then we use it. If our predictions are good, the model is useful. If they keep failing, we change the model. So models are not fixed. They are tools. We improve them by testing them against what we observe. Models can mislead. We might forget that the model is simplified. We might treat it as the whole truth. We might use it in a situation where it does not fit. So part of using models well is knowing their limits. When we pass knowledge on, we pass on the model and also the warning: this works when such-and-such holds; when it does not, we need to think again. What is a model you use? When does it work? When does it fail?