I think that's how most players do it, responsible. Either they have a pre-established threshold that they don't exceed, or maybe they exceed it a little but they are able to stop, leave and come back another day with a fresh mind to try their luck.
A strong emotion and mind is what they have. Whether they set threshold or not, they're aware when to stop and if it's necessary.
The problem is the problem gamblers, who don't stop at the limits and end up losing much more than they should.
The time will come that they'll realize that they should stop it when it should be. But as long as they still have money left on their pockets, they'll continue to gamble.
Until the time comes that they'll regret and telling themselves that they shouldn't continued and just stopped at all cost.