Gambling addiction is different from drug addiction in terms of reasoning from someone who is into it. Addiction in gambling is because people are dissatisfied with what they already won in a gambling, and tend to lose it all even if they know they are not winning the game.
This is true, but I also heard stories that it is actually more important that a person is winning for some time. If a person tries gambling for the first time and it is unsuccessful, this person is not likely to continue, because it is just boring. What keeps a person gambling is occasional winnings or anticipation of winning (brain studies show that winning and being close to winning during gambling are pretty much equally pleasant).
Some people gamble because they take it as their way on how to earn money everyday, some people take it as entertainment since they are bored in their life and some people take it since they love it.
Gambling for earning is different and it has nothing to do with addiction. I bet a gambling addict cannot be good at gambling. Addicted person is driven by emotions and feelings like pride, desperate decisiveness, anger etc. Look at the poker tours with top players like Negreanu. Even when he loses the game, he doesn't seek revenge and just says things like 'Oh, okay', 'No worries'.
One can be addicted to gambling simply because they are greedy and they want more money. That then results to a poor mental health condition.
But would a happy person eager money that much? Addiction is connected to mental health, but maybe this health was damaged by loneliness and distrust in the first place.