They are systematically taught to rationalize whatever it is they want to be so.
If they are suddenly confronted by an idea or concept that is new to them or is in direct conflict with what they currently believe, they are adept at finding a way to rationalize away any facts that make them uncomfortable.
I have JW relatives who haven't met their own grandchildren because their grown children left the "truth", yet when confronted, the will tell you that JW's are free to leave the organization without consequences . In their minds, they are telling the truth.