I have a friend who wins 15,000 pesos or $300 the first time keno games in an offline betting outlet, he is so happy and very ecstatic about his winnings, I congratulate him and ask him how long before he hit the jackpot, he told me that it took him 7 months and he is betting daily at 100 pesos or $3 so his losses are bigger than winnings.
But surprisingly he did not calculate his losses all he cares about is he finally wins, how about you do you remember your losses when you win a big amount and do you calculate your losses and ask if the winning is worth it?
I think the issue about your friend is not that he does not remember the loses he has made but really what can be done about it? He has lost it, it has gone and its never coming back. In short, its an historical cost which is irrelevant and there is nothing that can be done about it. So when people rejoices over a win (take away gambling now), it's not that they are oblivious of their losses but its about appreciating how long they have come, that they are not cut out for entire losses all the time, and there is hope again that winning might come in the future.
So, rather than making him feel stupid, I think you should support him to have his moment of rejoice then the next day, he can go back to do his costing.
