Don just provided examples of a good conceptual model. And an ineffective conceptual model, using the two refrigerators at Udacity. We’ll talk more about why the ineffective example, was ineffective in a moment. But first, let’s step back. And talk about what conceptual models are. So a conceptual model is an explanation. Usually highly simplified, of how something works. Sometimes conceptual models are inferred from a product itself. Sometimes they’re learned over a, a course of time. In other situations they’re passed down from person to person. They’re really good at helping people predict, how something will work. And what to do in case something goes wrong. I think conceptional models will like a lot more sense, if I provide an example.