The best sort of activity is one that combines mental effort with sensuous delight. That’s why I love drawing. The sheer physical pleasure of making a line with a good pencil on paper with enough tooth, or roughness, to put up a little resistance is inexhaustible; and the challenge of making the line resemble (as much as possible) the landscape, or still life, or face that we’re looking at is enough to put us on our mettle each time we try.