DO NOT RESPOND TO THOSE WHO CONTRADICT YOU.

You have to distinguish whether the contradiction comes from cunning or from vulgarity. It is not always obstinacy, but may be artfulness. Notice this, for in the first case one may get into difficulties, in the other into danger. Caution is never more needed than against spies. There is no such countercheck to the picklock of the mind as to leave the key of caution in the inside lock of the door.