An experimenter visits a preschool with a big box of magic markers and paper. The children are told that they can draw as many pictures as they want. The children enjoy the task very much. On another visit, the children are told that, for every picture they draw, they would earn a prize. Two weeks later when the experimenter returned, he offered up the markers and paper for play but said that no prizes would be given. The children played very little with the markers because extrinsic rewards can undermine motivation.