I am reading a book that was mentioned here a few days ago called Mistakes Were Made, But Not By Me. It explains why people tend to stay with a decision, even when they come across contradictory information. The more they have invested in a decision, the more they defend it and resist information that doesn't mesh.
They took two groups of college freshmen and put them through an initiation into a fraternity. One group had an easy initiation, the other group had one that was much more difficult. The difficult group were much more enthusiastic about their fraternity, more dedicated to it and less likely to notice or mention faults than the other group.
This is why it's so futile to attempt to get someone to leave the Watchtower, mist have too much invested. Most people have given up a lot to be JWs, this fact alone binds them to the religion, even when it makes no logical sense. It takes something fairly drastic to make a JW consider leaving the group. They have to be treated very unfairly, or have a family member treated unfairly, or face a personal crisis of some sort.