I am not sure sure about his happiness, but throughout his life, Giorgio de Chirico painted more than 80 versions of his Disquieting Muses, and at least 60 versions of his Piazza d'Italia. Clyfford Still is known for the curious fact that he almost always painted at least two versions of his large abstract paintings. Andy Warhol was notorious for producing big series of variations of one subject, such as for instance his self portraits, images of Marilyn Monroe, Campbells Soup Cans, etc. Claude Monet made many versions of the Haystacks, or of the facade of Chartres Cathedral at different times of the day, in order to demonstrate the impact of light on a subject. The German painter Arnold Böcklin painted three versions of his painting Iphigenie (19th century). The two versions of Goya's Maja (one with clothes and one nude) are interesting in this regard, too. One was "public", the other very private. Once, the two versions were installed on top of each other, so that the nude version was hidden, only to be revealed for special visitors. As you will see from these few random examples, there are literally countless cases of painters working the same subject over and over again, for a variety of reasons.

Claude Monet is known for painting several subjects repeatedly. One is a series of twenty-five canvases study of "Haystacks". He began it in the fall of 1890 and continued to the next spring. http://en.wikipedia.org/wiki/Haystacks_(Monet) Monet worked on a series of thirty canvases of the facade of Rouen Cathedral. This took place between 1892 and 1893.http://www.learn.columbia.edu/monet/swf/ Claude Monet also did many paintings of all his plants in his garden, waterlilies and poppy fields.