Why do loot boxes provide such a dark compulsion? Psychologists call the principle by which they work on the human mind ‘variable rate reinforcement.’ “The player is basically working for reward by making a series of responses, but the rewards are delivered unpredictably,” says Dr Luke Clark, director at the Center for Gambling Research at the University of British Columbia. “We know that the dopamine system, which is targeted by drugs of abuse, is also very interested in unpredictable rewards. Dopamine cells are most active when there is maximum uncertainty, and the dopamine system responds more to an uncertain reward than the same reward delivered on a predictable basis.”