Occasionally you win! Unless you own a casino, or are in any other way "the house." Then you always win. Seriously, even the games with the best odds, such as true Blackjack, or Craps, the odds are still in the house's favor. This goes double for online games. And if they think you're doing too well, they'll say they don't want your action, and ask you to leave.
Gambling, like everything else, if done in moderation, can be fun.