Opportunity Cost: This is the cost of forgoing the next best alternative when making a decision. In our analogy, the opportunity cost of eating salad is not getting to enjoy the pizza.
Cost-Benefit Analysis: This is an approach used to evaluate decisions by comparing their potential costs and benefits. If we continue with our food analogy, this would be weighing how much you value losing weight against how much you'd enjoy eating pizza.
Scarcity: Scarcity refers to limited resources available compared to unlimited wants and needs. Like having only so many calories you can consume in a day while wanting all kinds of delicious foods.