Things Great, Excellent, and Sublime
It is by no means to be denied that the man who subjects himself to studies too severe does violence to his nature; and, although he may sharpen his intellect on one point, yet whatever he does wants the grace and facility natural to those who, proceeding temperately, preserve the calmness of their intelligence, and the force of their judgment, keeping all things in their proper place, and avoiding those subtleties which rarely produce any better effect than that of imparting a laboured, dry, and ungraceful character to the production, whatever it may be, which is better calculated to move the spectator to pity than awaken his admiration. It is only when the spirit of inspiration is roused, when the intellect demands to be in action, that effectual labour is secured; then only are thoughts worthy of expression conceived, and things great, excellent, and sublime accomplished.
Giorgio Vasari, "Paolo Uccello" in The Lives of the Most Eminent Painters, vol. 1, Lavin, ed., Heritage Press (New York: 1967) p. 107.