A big loss is a big loss because it is the amount of money that you cannot afford to lose and it must affect you negatively. Some people might have used the money given to them to keep in their custody to gamble. Some use their Boss funds to gamble and lose it all. It becomes a big problem for them to tackle. This is why we see some gamblers commit suicide for not being able to cope with big loss.
That's one case of a bad gambling addiction, when it gets to that point, the person needs to seek for help so that they don't land themselves in a bigger problem because since such people lack self control, they might not be able to control their self even if they have to borrow and keep borrowing just to gamble, they will do it. Such person can not easily forget about their losses because it will continue to using it as an excuse of chasing more wins.
However, I think it is too common for a player to chase losses, I have experienced this myself, until I realized that many players have this problem. In fact, gambling establishments even benefit from players behaving this way and losing control, because the speed of loss accelerates and when a player wants to win back again, he will need to borrow or borrow money somewhere else, which takes addiction to a new level. In general, when we start to come up with excuses to play, at this point we need to stop, but the problem is that no one thinks logically anymore, because emotions completely take over the player.