I run into this at work all the time.

Me: FYI, in scenario xyz, I updated the documentation to do abc. It seems like the best balance of complication and doing the right thing, especially considering it will almost never come up.

Boss: why does it even matter what it does? It will come up maybe once per year. Oh, and it should do <this other really specific and complicated thing> instead, so do that.

Me: sigh....

Maybe you can explain it to them this way - if they know what a function is. If you have a function that does something, foo, and it takes one boolean parameter, that's two test cases. If you add a second boolean parameter, now you have at least four total test cases. And so on.

Ah yes, give it to them in functions and boolean parameters, that will get the non-programmers on board. /s

My house has a vacuum, a lawnmower, a blender, a washing machine, 20 light switches, a 4 zone heating system, and 6 sinks/showers. I can manage 1.71e10 possible states while I sleep, why are you struggling with four?

well, a binary order of magnitude maybe

Indeed. There was a paper done in the 70s or 80s that found that operating system size doubled with each new feature. Picture going from single tasking to multitasking or to virtual memory. Sorry, I cant dredge up the reference.