I personally feel that the key to open-mindedness is to recognize that your beliefs shouldn't be concrete certainties, rather they need to be probabilities that are based on all the available data and evidence that you have access to, and these should shift as new data is acquired or debunked. Otherwise, you can simply ignore all evidence that contradicts your viewpoint creating an unhealthy confirmation bias.
Most JWs don't view things in this manner, they KNOW (or at least feel pressured to openly claim that they know) that they alone have God's backing. Or more accurately, the organization they are a part of has His backing. It's very common for a conversation with a Witness to lead them talking about how "glad they are to be in the Truth," or how they can't wait for some promise that they read in the Watchtower to be fulfilled in the "new system." And if one has doubts about those things and openly expresses them, they are held to be "spiritually weak" which is the greatest of sins in JW Land. Even genuinely agreeing with someone else about the uncertainty of your own beliefs is considered spiritually weak, which, to the indoctrinated, makes them feel guilty themselves even if no other JWs are present to make them feel that way.
