The commonest error of the gifted scholar, inexperienced in teaching, is to expect pupils to know what they have been told. But telling is not teaching. The expression of facts that are in one's mind is a natural impulse when one wishes others to know these facts, just as to cuddle and pat a sick child is a natural impulse. But telling a fact to a child may not cure his ignorance of it any more than patting him will cure his scarlet fever. (p. 61)