The most important presupposition for JWs is that the GB is guided by Jehovah through his holy spirit. Everything they say is good/right/true because it is from god, not men. Any guidance they offer and any interpretations they make are thus divine and questioning them can be a sign of apostasy.
The potential problem is with their admission that they're imperfect men and don't always get things right. The implication is that god always gives them the right guidance, but they are flawed humans and don't always figure out the message until much later. But this makes it look like either god is not good at getting his guidance through to them, or they are bad listeners. Either should make even a loyal JW go "hmmm..."