To use gambling as a means to earn a living.
Not everybody can do this, but a minority can. These are the professional gamblers. Professional gamblers literally gamble for a living. How is that possible, you say? How can you make money from a gamble? Well, what these gamblers do is they cut the gaming part out of the games they play as much as possible. Games of skill which bring positive results - video poker, poker, blackjack, craps - are what the pros like to play. When you gamble in this way, you are not really gambling like ordinary folks do. You're playing for money. Actually, it's a very cool job if you ask them!
Those professional gamblers, besides from their gambling strategy in skill based games, also have enough bankroll to cover all the possible win-loss ratio. If you are just gambling with small amount and playing it for fun, much better stick with that idea because in pro gambling, all are serious in gambling world.