Plato Charmides 173

For in truth, let temperance be ever so much what we say it is, I see nothing 173a to show what good effect it has on us.
  How so? he asked: tell us, in order that we on our side may know what you mean.
  I expect, I said, I am talking nonsense: but still one is bound to consider what occurs to one, and not idly ignore it, if one has even a little concern for oneself.
  And you are quite right, he said.
  Hear then, I said, my dream, whether it has come through horn or through ivory. ¹ Suppose that temperance were such as we now define her, 173b and that she had entire control of us: must it not be that every act would be done according to the sciences, and no one professing to be a pilot when he was not would deceive us, nor would a doctor, nor a general, nor anyone else pretending to know something he did not know, go undetected; and would not these conditions result in our having greater bodily health than we have now, safety in perils of the sea and war, and skilful workmanship in all our utensils, our clothes, 173c our shoes, nay, everything about us, and various things besides, because we should be employing genuine craftsmen? And if you liked, we might concede that prophecy, as the knowledge of what is to be, and temperance directing her, will deter the charlatans, and establish the true prophets as our prognosticators. Thus equipped, the human race would indeed act and live 173d according to knowledge, I grant you (for temperance, on the watch, would not suffer ignorance to foist herself in and take a hand in our labors), but that by acting according to knowledge we should do well and be happy—this is a point which as yet we are unable to make out, my dear Critias.
  But still, he replied, you will have some difficulty in finding any other fulfillment of welfare if you reject the rule of knowledge.
  Then inform me further, I said, on one more little matter. Of what is this knowledge? Do you mean of shoe-making? 173e Good heavens, not I!
  Well, of working in brass?
  By no means.
  Well, in wool, or in wood, or in something else of that sort?
  No, indeed.
  Then we no longer hold, I said, to the statement that he who lives according to knowledge is happy; for these workers, though they live according to knowledge, are not acknowledged by you to be happy: you rather delimit the happy man, it seems to me, as one who lives according to knowledge about certain things.