You can't depend on the business people to understand the business logic clearly enough to explain it to the implementers. That will never happen. They may understand it themselves, but they're not coders and they can't write requirements for code.

Instead, at least one implementer needs to get hands dirty on what the application space really is. Very dirty. So dirty that they actually start to really know and care about what the users actually experience every day.

Or, more realistically for most companies, we insist on separate silos, "business logic" comes to mean "stupid stuff we don't really care about", and we screw around with if statements. (Or, whatever, we get hip to monads and screw around with those. That's way cooler.)