The people who do better and better work are people who are never satisfied. Cezanne would say, 'I think I've accomplished something,' but then he would immediately add, 'But it's not enough.
Artists who have produced experimental innovations have been motivated by aesthetic criteria: they have aimed at presenting visual perceptions. Their goals are imprecise, so their procedure is tentative and incremental.
Experimental artists build their skills gradually over the course of their careers, improving their work slowly over long periods. These artists are perfectionists and are typically plagued by frustration at their inability to achieve their goals.
The precision of their goals allows conceptual artists to be satisfied that they have produced one or more works that achieve a particular purpose... a problem solved can free him to pursue new goals.
Titian and Rembrandt, Monet and Rodin, Frank Lloyd Wright and Le Corbusier, Mark Twain and Henry James, Robert Frost and Elizabeth Bishop, to name a few. Twain wrote 'Tom Sawyer' at 41 and bettered it with 'Huckleberry Finn' at 50; Wright completed Fallingwater at 72 and worked on the Guggenheim Museum until his death at 91.