If you are a gambler, controlling yourself is easier said than done. You will leave your ATM card at home and bring only certain amount to gamble but if you lose you go home and get that ATM card and go back to gamble hoping that you will regain that lost money only to lose more. Have experienced this kind of scenario, self control is very hard when you know that you still have money back home.
True, once we become a gambler, it'll be hard to stop it right away. But by bringing only small part of our money while we gamble, at least we still have time to think whether we want to risk the other money or not. The decision may differ from each person.
I wouldnt call that a gambler, rather a problem gambler. Most casino users are gamblers and dont go so far.