JDKJ said:
A) Because when you play against a house, like a Vegas casino, the house has structured the game so that is has an advantage to them called an "edge" (in some poker games the "edge" is as much as 5%). This means that over time and if you play against the house long enough and no matter how skilled you are at poker, you will, over time, lose to them. You can bet on that (pun intended). You may win big today, but if you come back tomorrow and continue playing, eventually the house will win back its money plus some of yours. It's bound to happen as a matter of probabilities because of the "edge." If the casinos didn't structure their games like that, then there would be absolutely no guarantee that they wouldn't go broke within a year of opening their doors because players won more from them than they took in from players. And the house ain't in the business of going broke. They're in the business of taking money away from players.
Therefore, playing poker against the house is a game of chance. No matter how skilled you are at playing poker, there isn't a thing you can do to stop the inevitable outcome that over time the house will win and you will lose.
Unless you're playing some carnival type table game like Caribbean Stud or Let It Ride or some such thing all live poker games at the casino are not played against the house. The house makes it's money off of a rake where it takes a small portion of each pot. However, despite the rake, you are playing against other people, not the house.
There are people that make money week in and week out at casinos and are repeatedly welcomed back. In a live game of poker (Hold em, 7 Card Stud, Omaha, etc) at any casino the casino has zero vested interest over who wins and who loses. They get paid all the same. There is no house edge at a live game of casino poker. There is only a rake per pot and that is common in any typical game of poker. I've even been to home games that take a rake to pay for food and beverages.
Now if you are talking table games like Black Jack, Caribbean Stud, Let it Ride, Craps, Pai Gow, Three Card Poker, Red Dog, Baccarat, etc then there is always a house edge that fluctuates as high as 20+% on some games to as low as 1%. These are the games that can not be won over the long term. However, live poker, can and is profitable for many regardless of the venue you play at. The only difference between a home game of poker and a game of poker at a casino is typically there is a dedicated dealer and the chairs and table are a lot nicer.