This question has always intrigued me. Most economists believe that we do things in order to increase our utility. This only raises a question about our definition of utility. Art thieves take great risks when they steal paintings from very secure museums. The paintings are worth millions but they cannot easily be sold for anything near their market value. Why to they do this? This article was written by an author who has written a book on the subject. He tells us that many of them do this to demonstrate their skill as a thief. Apparently, a job well done is their reward.
This reminds a bit about a comment attributed to Steve Job's. He claimed that his purpose was not to become the richest person in the graveyard. He had nothing against earning large sums of money, but that was not what really motivated him. Developing great products and building a great company was what pushed him to devote his life to that purpose.