Epops: The wise can often profit by the lessons of a foe, for caution is the mother of safety. It is just such a thing as one will not learn from a friend and which an enemy compels you to know. To begin with, it's the foe and not the friend that taught cities to build high walls, to equip long vessels of war; and it's this knowledge that protects our children, our slaves and our wealth.
Leader: Well then, I agree, let us first hear them, for that is best; one can even learn something in an enemy's school.

Birds (414 BC) [tr. O'Neill 1938, Perseus]