Imagine the scenario: you have fulfilled your dream by buying a McDonald's franchise. You start hiring employees and come to realize that the first employees you hired were extremely productive, but every additional person you hired seemed to be less productive. Why does this occur? Are the last people you hired just lazy?

So far, I have "Employees can seem less productive than the initially hired ones due to a variety of reasons other than laziness. The law of diminishing marginal returns can best explain why this phenomenon occurs." Could you help me elaborate a bit on this or even adjust it to make it more accurate if possible? Thank you!!

(trying to expand answers, if you've answered please skip thank you)