you can earn millions with gambling if you are extremely lucky though it is nearly impossible to not loose everything you have to do it
The most predictable scenario is to win zero
Winning zero should be OK but mostly addicted gamblers will lose all their money in these gambling sites. That is most worst part in gambling because every one knows before starting gambling that they can't win or make profits from these games but still they want easy or free money so end up losing all there money in gambling.