1. People who have suffered from a serious gambling addiction and recovered (so they have some insight into their problem)
2. Psychologists who have researched and/or treated people with serious gambling addiction
For most of us, who are not these people above, it is just guessing.
But... if I am allowed to guess on this thread (and I think that I am
![Wink](https://bitcointalk.org/Smileys/default/wink.gif)
(i) being psychologically more likely to develop addictive behaviour
(ii) having difficulties in your life (economy, family, work issues, etc) that trigger this behaviour
One thing I know - it is a terrible and destructive thing to see happening to a person.