In Econ 101 textbooks, there are lots of examples and emphasis on marginal analysis leading to the greatest equation of all, $MB=MC$.
My challenge is the following and wonder if anyone had a similar issue or a way to get over it:
One of the textbooks examples use consuming pizza or water. First unit brings you the biggest joy. Then it diminishes. So student would understand each additional unit of pizza wouldn't bring the same amount (e.g. initial v. when you are full) utility. But then there comes a time where you are quite full and feel satisfied. At this point, additional unit of consumption would probably make you feel sick or vomit, so it is not "worth the money" to spend on.
The trouble with this example is that it illustrates at margin, benefit is not constant. There comes a time when you would stop consuming. But this doesn't really shed light on why $MB=MC$? How can I do a better job explaining that this "equality" is embedded in all these stories? Is it perhaps the stuffed/eat-until-vomit is a corner solution example?
For pedagogical reason, if you are better at explaining these concepts, please share how you would go about this with an example both interor and corner solution in ECON 101 textbook situation.
My strategy was from example to the graph and to show why the equality should hold leading to connecting the dots on the first order conditions of utility maximization... But this equality is hard to really spell it out on 101 level, that's my challenge.