It is at this point that he is supposed to understand that they are going a bit far according to Op. If they don't retrace at this point, they are heading straight to addiction which is the extreme of it all.
@Zoomic, don't get it wrong first, being self disciplined does not mean you should not engage in gambling, also not all gamblers are undisciplined, we have people that doesn't gamble but have the highest order of indiscipline, this is an individual responsibility to take care of, if you think you want to gamble, you can chose to have a disciplined lifestyle with your gambling or not to, also for every undiscipline gambler comes addiction following, because they will always want to behave the way they want at any cost not minding what others may say.
That gamble that is discipline will always know when to stop gambling for that particular day. He will also know how much attention to give gambling and how much to give his work and family he will set out budget such that whenever the budget is exhausted, he will stop. But there is another level of discipline which I have also highlighted because you mentioned gambling is for entertainment. So a highly disciplined man should rather look for other ways to entertain himself rather than gambling. @Fredomago understood me better.
I got your view, being undisciplined can occur at any settings be it in gambling or on other field that has to involve people relating to each other, which could also qonote that gambling is but the highest order of where indiscipline can be achieved, people set the pace for being disciplined in their own capacity to avoid any unnecessary impression below the expected target they so desired to arrived at, we need to call ourselves back to order if we noticed strange behaviors in our gambling experience, take an effective control measures and make moves to apply them as rescue, this may not have to be with gamblers alone, anyone can fall a victim and we can observe this before things get outrageous.