Reason and free inquiry are the only effectual agents against error.

Two things are named, and the second gets neglected. Reasoning well is not enough on its own if the questions you may ask are limited, because an error protected from examination can survive indefinitely inside perfectly good logic. Open inquiry is what exposes the assumption that was never up for discussion.

In any group you belong to, notice what cannot be asked without a cost. That is where the mistakes are stored. You do not have to be the one who raises it every time, but knowing where the closed area sits will tell you more about the group than anything it states openly.