"It is not possible, however, for the same thing always to give pleasure, because our nature is not ismple: it contains a separate element which renders us mortal, so that wehn one of these elments is active it is counter to the nature of the other; and when they are exactly balanced, the effect is something that is not felt to be either painful or pleasurable."
Aristotle, The Nicomachean Ethics, 1154b lines 22-27