One major thing that has always ruined gamblers is greed.
Greed is part of human nature so it's expected that most of the gamblers has that attitude but it will only matter on how each of us can control it. And with gambling, it's all easy money so those who found fortune with it are looking to it as a profession.
The key thing in gambling is to have a set goals or plan, how much you intend to stake (total sum) and how much loss you can accommodate. Once these two is set, then you have to gamble with your head intact and not emotionally. Quite a lot of people depend on it for survival though.
Right, it's about the control and goal setting. Also the same in trading, it's okay to stop loss if it is needed.