I would say I had a mild gambling addiction in my first two years of university. I played far far to much poker, and bet on sports to much.
I was never that serious that it ruined my life, or caused any major drama.. but it took away large chunks of my disposable income for a couple of years.
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My problem was the internet and self-control. in both cases, I started playing in person in real life.. I was very good at poker in person, and won a decent bit of money in university and in poker clubs. Betting wise, I usually broke even or ended slightly up when going to betting shops.
But that all changed when I started to do both online. I had terrible self-discipline back then, and its something that I have worked very very hard to improve now, to the point where I would say I am very disciplined. In real life its easier to impose limits. So for example when I played poker in person.. I would go to a poker club, sign up for 1 or 2 tournements.. 30-50 quid a pop. or I would play a cash game for 100-200 pounds. Both of these have defined end-points.. the tournements end either when you win, or loose, and whilst some let you add more cash, they still always end after a number of hours. The cash cames were easily limmited by how much cash I brought with me.. as I never ever used my card. So worst case scenario was I lost a limmited amount of money.. say 100 pounds in a night, and it could never be more then that. I felt awful, went home.. chilled out, and then only went back when I felt better again. Often nights would be winning nights, and overall I did very well.
The problem with online is that it was 24/7 and there was always a game, and its always tied to your card, and the limmits are entirely self-imposed. So I would play.. and win sometimes.. same as in person. But if I lost - I didn't need to go home because there were no more games that night, or because I didn't have cash.. If I lost I could play again and again and again, getting more and more frustrated, and playing worse and worse due to the negative emotions.
So over the two years or so that I played, I ended up winning a fair bit in person.. but loosing more online. Then I decided to stop, which co-insided with me meeting my now-wife and focusing on turning my life around. The biggest thing that helped me stop playing games though was starting my own business, and very quickly realising that I can earn far more reliably through being clever and working hard, then I ever could from gambling. Sure I may not have the chance to get millions yet, as is possible when you gamble.. but I can reliably bring in plenty of money now.. which still gives me a great feeling, especially when its my work, for my company thats bringing me in an income and plenty of cash - but it carries far less luck and risk then gambling did.