I think many of them known or have an idea on how much they're going to lose but they just turn their eyes blind when they're already losing.
Ego is hard to beat and recovering is much easier to think of than accepting the big losses that someone might have.
Those that can't track their losses or don't really track at all, many gamblers do that. They're having hard time in figuring out how much budget they will do to gamble.
That's when they go too far because at this rate they cannot stop themselves anymore when they use the money they aren't supposed to. Others are moderate when it comes to their gaming and that can also lead to addiction for others especially if they develop hyper-excitement when they are playing this happens to lots of people when they have lots of buddies who often play with them because it's not a matter of habit anymore, it becomes a matter of prestige and merit on who will gonna win big and they compete with that without taking precautions of the consequences in their future.
Rightly said that everyone knows that the risk in gambling is high so gamblers should know the positive and negative aspects of gambling well. If you can't control yourself it will lead to more serious problems if it becomes a habit it is the excitement of gambling that drives more than financial gain. Most of the time is passed by gambling or thinking about gambling all these reasons are ready to make big bets day in and day out in losses. Therefore it is better to have a clear understanding and be alert to the potential risks of this activity.