Maybe the point is that you tend to overlook the total cost because of the small cost per event and because you are conditioned to accept the cost as a necessary evil.
IDK, but I do know that managers love those kinds of justifications.
In that case, it's a question of attitude, not (simple, ridiculously obvious) equations. Why is it called 'math', much less 'manager math', when it's really about being stingy?
His point was that little costs can add up, and help you make the case that a big cost can actually be a cost savings.
You see this happen a lot, especially with costs that are sunk, like salaries. I don't know how many times I've seen the choice towards increasing workload and staff - even though it costs more than just buying a better piece of software - being made.
I'm not sure of your background, but obviously this post isn't aimed at you. If you've ever had to sit around a table at budget time however, it's pretty much a given that a good deal of people aren't able to do "manager math".
Am I missing something important? Is it a parody?