It's the same as dealing with a human. You convey a spec for a problem and the language you use matters. You can convey the problem in (from your perspective) a clear way and you will get mixed results nonetheless. You will have to continue to refine the solution with them.

Genuinely: no one really knows how humans work either.

It's actually no different from how real software is made. Requirements come from the business side, and through an odd game of telephone get down to developers.

The team that has developers closest to the customer usually makes the better product...or has the better product/market fit.

Then it's iteration.