The Negative Return of Gambling, by Dan Grossman
When I took Skinner's coarse in behavioral psychology, the pigeons invested their time and energy by pecking at a button which (sometimes) triggered the reward of a pellet of food.
The pattern of reward was varied by the experimenter, for example:
Random reward, which is the closest to a game of chance, caused pigeons to play the longest and most energetically. It is the random reward, including as Martin says the possibility of a large payoff, that is equally exciting to humans, especially those that like to play games of chance and games of mixed chance and skill.