Being greedy and overly trusting in gambling for sustenance is a bad concept and every gambler must make sure to avoid those features since they are the partway to possible addictions in in the long run.
It's easy to say this but in reality, it is almost impossible to convince the gambler that he is addicted to gambling and even more different to ask him to quit gambling. The gamblers don't care what is good for them in the long run, they only see the present and want to earn money through gambling.
I don't think it can be easy for anyone to quit gambling. One situation can be that the gambler loses everything and become out of cash, only in that case he may quit as he has no other option but other than this, I don't see gamblers quitting.
Well , I think you totally missed the what Wiwo was pointing out in his comment, he wasn't talking about how easy or difficult it is for gambling addicts to quit or not quit gambling, and he wasn't also talking about whether it be impossible or not, for them to agree that they are addicted to gambling.
What Wiwo is saying is that gambling for sustenance, that is depending only on gambling as a source of livelihood is a bad attitude or character, and it is one the common ways by which many get themselves addicted to gambling, since they think of nothing else other than gambling.