Cameron gets a new job at a greeting card store and loves it because he is able to buy greeting cards with the employee discount. This greatly increases his greeting card purchases, and Mitchell points out that it is not saving them money, but costing them money. The discount represents a price reduction, which causes Cam to increase the quantity of cards he purchases. This can also be seen as a form of mental accounting where Cam prioritizes the savings instead of seeing the cost of each card.
See more: demand, income effect, mental accounting, nonpecuniary benefits, prices, quantity demanded, rationality
When Mitchell realizes how cheap items at CostCo are, he suggests getting enough for the next two years. When he realizes how many diapers that is, he thinks about getting a shed to store them all. When people face steep discounts on prices, they respond by buying more (law of demand), but how much more they decide to buy is based on the elasticity of demand. In this case, Mitchel appears to be a very price sensitive buyer even though the items are really necessities.
See more: complements, demand, elasticity, income effect, prices, quantity demanded