I have one friend who was gambling addict before, he is mid-class guy (average incomes, not something too high, neither too low) and he gambled about 30.000EUR in casino.

He started gambling for fun when he was around 16-17, firstly he gambled small amount of money like 20-30EUR per session, sometimes he earned some money, sometimes he lost his money, but he somehow get addicted then. Now he is 23 years old, but when he was like 19 or 20, me and few friends of mine went to one trip all together. When we arrived at that city we went for nice lunch, and then our friend went to casino (we tried to convince him not to go since he was addicted already, by that time he already lost like 20.000EUR), but he still went to casino. He deposited like 100EUR (something around that), and he managed to get around 1.500EUR. Me and my other friends went for dinner (while he was in casino), and then he came back home and said to us that he will take us tommorow to nice dinner etc. because he "earned" 1.500EUR. I kept telling him before to stop gambling, since he is not gambling responsive, but I thought to myself - alright, at least he is not losing money, actually he withdrawed nice amount for cash (good amount for starting capital).
Everything was perfect, but next day, when we was about to go to dinner, he refused to go. We asked him why is that, and he said to us that because of that nice win, he couldn't sleep because of overthinking about that "big" win, so he went to casino and gambled all away. We got in a beef with him then, not because of money of that dinner, because how stupid and addicted he was. Also to mention, how I borrowed him few grands of EUR, thinking he will spend it for something good, he was telling me that he need money for car parts etc and obviously he gambled it away. I said to him that I will not only borrow money to him, I will not talk to him unless he get professional help from therapy. About year ago, when I got sure he is fully healed from that addiction, and he is not gambling anymore, I started talking to him again.

Gambling addiction is so fucked up because of 2 reasons; 1. you are guaranteed to lose money, since mathematically you are losing money over long-run (casino house-edge), 2. your mental is fucked up as well, you are never happy or in a peace - if you are winning money, you are chasing for a big win or if you are losing money, you are chasing your losses.

Imo gambling can be alright if you REALLY know what the hell you are doing, but if you are not responsible it will easy drag you away. (like once in a while, bet on your favourite team to win or something like that.)