Sometimes things have been trundling along on so much fuzz and handwaving that nobody actually knows how things are supposed to work when it gets down to formalizing them into a set of rules that could be implemented in code. Many such cases.
If someone doesn't understand something it's because it's either not been explained well enough or that person doesn't have the background necessary to understand it. Either they need more information or they shouldn't be making decisions about it.
If the problem is that the issue hasn't been explained well enough then the developers need to work harder to better explain what the problems are and why they're problems.
If the problem is that the business person doesn't have the necessary background to understand the issue then you have a huge problem. That person is going to be a problem at every step. I don't envy anyone in that situation. In the past 25 years of development I've never actually encountered that situation though.
I’d put forward that there’s one more possibility: the person’s paycheck is contingent on them not understanding.
Unfortunately, some business people are compensated as direct function of revenue (growth), even though they have to pull engineering levers to obtain that delta in revenue.
For a lot of these people, once they’re convinced that doing X will lead to growth, no explanation will convince them that it isn’t worth it.