If someone wants to believe, they're going to believe. You can't change their mind no matter how logical, factual, reasonable you present the message. This is true in a lot of areas, not just religion. But when they're indoctrinated into a cult religion, not only are they close minded on their own accord, they're influenced by the leadership to be even more stubborn and steadfast.
Not to say it can't be done, but if you're going to try to open someone's mind, you're going to have to tailor it to that specific person and their particular hangups that you can take advantage of.
I learned the hard way to not be aggressive or to be too critical. It only makes them defensives and they get their back up. You have to let the moment come to you. Sometimes it doesn't happen for while, other times it drops in your lap as if you planned it. Let the natural course of events take place, but when something happens or is said that flies in the face of the WT-think, you can pounce on that and push it to the edge to see what response you get. Sometimes you make progress, sometimes they shut down. I've actually seen the JW's eyes glaze over when I reached critical mass when pushing the edge on a discussion, pointing out the illogical and delusion of believing in certain WT fantasies. That was probably too far, but I think it settled somewhere in the recesses to come back later.
Letting outsiders influence a JW helps too. The key here is to have a life outside of the four KH walls. If they only ever associate with JWs, they may never learn to think for themselves. But get them out of that setting, realize that 'worldly' people aren't so evil and they start to enjoy the outside life. In time - and it does take patience in this strategy - they become less JW and more normal. They may still have some deep held JW beliefs, but on the surface they're letting go and moving into a more normal way of life. Sooner or later, the two worlds collide and discomfort causes them to hopefully meditate on what is causing it. Their eyes open to their own cognitive dissonance, and the real escape can begin.
