There's a study on this... I o py remember it pretty vaguely, but the tl;dr was that if people win at gambling it doesn't hold much appeal -- the initial drive to continue gambling only comes after losses. Something about 'making up for' anything you lost drives the addiction behaviour far more. This struck me initially as kinda counter-intuitive (you'd think that people were more motivated by behaviours with positive outcomes, right?) so it always stuck in my head...