There are philosophies which, however difficult they may be, are in principle easy to teach and to learn. Of course, not everyone can teach or learn philosophy – any more than higher mathematics; but the philosophies of certain philosophers have this in common with higher mathematics: they present the simple alternative of being either understood or not understood. It is, in the last analysis, impossibile to misunderstand them. This is true of Aristotle, or St. Thomas Aquinas, or Descartes, or Locke, or Kant. Such philosophies are like mountains: you climb to their tops or you give up; or like weights: you lift them or they are too heavy for you. In either case you will know what has happened and ‘where you are’. But this is not so with the thought of Plato, or St. Augustine, or Pascal, or Kierkegaard, or Nietzsche. Their philosophies are like human faces on the features of which are inscribed, disquietingly, the destinies of souls; or like cities rich of history. ‘Do you understand Kant?’ is like hasking ‘Have you been to the summit of Mount Blanc?’ The answer is yes or no. ‘Do you understand Nietzsche?’ is like asking ‘Do you know Rome?’ The answer is simple only if you have never been there.
[Erich Heller, da Wittgenstein and Justice, Hanna Fenichel Pitkin,
University of California Press, 1972, p. viii]