Believe it or not, winning actually contributes the majority of the stimulants when it comes to gambling. It is also why, after winning, people become drawn to gambling or, in the worst case, become addicted, it's just that it doesn't affect different people the same way. There are people that doesn't really get the urge to gamble again even after winning a lot of money, and there are people who do get affected and get the urge to gamble again when they win, just to try their luck again.