As long as they can produce money they will go for it. Last night I was amazes on those people that I'm playing with in a machine roulette in a land based casino. I see them betting big and winning huge, but at the end, they lose everything. However, I will just hear them chit-chat for a new minutes as if nothing happens. And then one of them will go down, and return with huge amount of money. I don't know where this guys get their money, maybe I have few speculations. But I can't believed them not stopping when they have huge winnings already.
That's because these people have become accustomed to losing. I think that the people who can so easily lose a crazy amount of money without showing emotion afterwards (in relative terms) are probably the problem gamblers. Any person losing a large percentage of their net worth regularly and still continuing has a problem.