Not only victory overshadows them but also defeat, when they continue to experience defeat then the brain will represent an ongoing emotional form. And when their emotions subside, then they will continue to fantasize if they win big then they will be rich, that's what humans are like. The thing that I think is good for gambling addicts is hypno therapy so that their brains return to normal.
Actually even defeats aren't the right reason for the gamblers to stop gambling because there are still players who are still playing even up to the point that they are consistently experiencing failures because of the addiction they have. They cant stop because for them if they stop there is no chance for them to stood up from tgeir loses. I know that because I m a gambling since then.