Marginal costs exist because:
households and businesses make rational decisions.
most decisions do not involve sacrifices or tradeoffs.
the decision to produce more of some product means the sacrifice of other products.
marginal costs don't do what marginal costs do for marginal costs but because marginal costs are marginal costs!

You work as the sales manager for a company that sells office supplies to businesses of all sizes. because the profit margins are razor-thin, you need to ensure that you are getting the very best prices on paper, pencils, pens, post-it notes, and other office supplies from the manufacturers. when reviewing the quarterly profit statement, you realize that your costs are higher than they should be, and you trace the higher costs back to an employee who has been lax about getting competitive bids to ensure the lowest prices. when you conduct your research to determine the reason for the higher costs, and take action to bring those costs back down, in which of the key management processes are you taking part?