That gambler wins a jackpot so he won from casino. But he need to think how much money he already used before he won? If his losses is less than his winning, that means he win the money.

But if their losses money is bigger than their winning, they still lose the money. That can attract them to continue gambling and spend more money without calculation. We don't have to feel too happy and compare the losses and the win so we know the truth. But still, win a jackpot make us forget our losses before.