Final answer:
The principle you are considering when assessing the cost and satisfaction from a cup of coffee is marginal utility, which indicates that satisfaction from additional units decreases over consumption. This is tied to opportunity cost, which is the value of what you give up when you make a choice.
Step-by-step explanation:
When weighing the cost of a cup of coffee against the satisfaction you will obtain from it, you are taking into account the economic principle of marginal utility. This principle explains that as you consume more of a good or service, the utility, or satisfaction, that you derive from each additional unit tends to decrease compared to earlier units. For instance, the happiness you experience from your first cup of coffee in the morning might be high, but as you consume more, the additional satisfaction you get from each subsequent cup diminishes.
This concept is closely related to the opportunity cost, which measures the cost of what we give up when we make a choice. If you decide to buy that cup of coffee, the opportunity cost is what you could have done with that money instead, such as purchasing a different drink or saving it. Thus, rational consumers will continue to purchase additional units of a product as long as the marginal utility from the product exceeds the opportunity cost.