Rule number is very important, some delusional people call themselves professional gamblers, all they do is rely on gambling without having a source of income. Trying to make gambling a source of income is a quick way to poverty. Just like you said anyone that wants peace of mind wouldn't make such a stupid mistake, gambling can't be a business or some kind of investment. it's a game of chance and luck.
Indeed. It can't be a way to earn stable income since many gamblers are not fortunate to win. But some of us are not thinking and still risking their money for the hope it is the answer to become rich. Gambling is a game of luck and only few gamblers had a life changing win through it. It's not wrong to try but don't expect too much to the point you'll use your money (that you can't live without) just to try your luck. Thus, before playing, be aware of the risk so you can prepare yourself.
Only few can take advantage, as we all know that most gamblers become greedy when they start to feel the confidence that they can make money from the casino, unable to realize that it's just a tactics that casino do to bring them in and keep them gamble, along the way casino is a business and they plan it all along and they knew gambler will be out of luck and after that they will just continue collecting money from each gamblers that will use their services.
It is not impossible to win in a sustained way for a period of time, but it's definitely more exceptional as wins pile up and time passes, and I don't think most casinos will let someone so lucky keep playing, whether it is because of pure luck or not.
Although it is almost impossible, I think that it is easier to win a great jackpot that pays you enough to live, than to make a livelihood from gambling like the "professional gamblers" you mentioned.