Rhetoric is useful because the true and the just are naturally superior to their opposites, so that, if decisions are improperly made, they must owe their defeat to their own advocates; which is reprehensible. Further, in dealing with certain persons, even if we possessed the most accurate scientific knowledge, we should not find it easy to persuade them by the employment of such knowledge. For scientific discourse is concerned with instruction, but in the case of such persons instruction is impossible.
AristotlePerhaps here we have a clue to the reason why royal rule used to exist formerly, namely the difficulty of finding enough men of outstanding virtue.
AristotleIt is possible to fail in many ways . . . while to succeed is possible only in one way (for which reason also one is easy and the other difficult - to miss the mark easy, to hit it difficult).
Aristotle