If only customs were logical. If only the rules were as simple as "Don't do anything that will hurt others." If that were the only rule, I’d have at least a fifty percent chance of getting it right. I would, for example, ask myself whether saying the Rosary silently on the train would hurt others. The answer would be no and so I would say it. As it is, the reasons as to why something is right and something is not seem arbitrary.