Ok so more broadly mal i think there are a few different types of gambling.
(some people will know a lot of this, probably better than me, so chime in if i am wrong)
Pure Chance GamesPokies, Roulette, Craps, etc. I dont think we really need to discuss these, as i think most people on here would realise you can never win in the long run playing these games. People like to think about systems in roulette where they try to bet on numbers that havent come up, or similarly on poker machines that havent paid out, but the fact is they are purely random and they pay back less than the odds. So in the long run there is absolutely no way you can win. (we wont talk about thinks like unbalanced roulette wheels which are just sidebars)
The key thing here is to remember that each trial (be that a spin, a roll of the dice, etc etc) is INDEPENDENT of the previous ones. This is called the gamblers fallacy
http://en.wikipedia.org/wiki/Gambler's_fallacySports BettingSports betting is interesting as it is probably the one most of us think we have a good shot at.
To keep it simple we will think of a footy game with only two results but it follows for other events with multiple outcomes. Simply, the house is trying to set the odds so that an equal amount of money is wagered on both sides, and they will set the odds slightly lower than what they believe to be the actual likelihood. this creates a house fee, juice, whatever. typically 5-10% for a head to head game.
This means that if the odds are set correctly, theoretically there should be an equal amount of money on both sides, and the house cannot lose - they take their 10% and be on their way. Of course if one side is bet more heavily than the other they stand to win or lose much more than 10%, but they will usually adjust the odds accordingly so this does not happen (think of horse racing where they do this on the fly)
So...
in a two horse race, for a punter to win they would have to be right more than 10% above average. so they would have to correctly deduce the winner more than 55% of the time to make money, if the juice is 10%.
The debate comes in as to whether any person can do this in the long term.
I think the answer, for the average punter, is highly likely to be no. The most knowledgable people who bet huge money influence the odds that much that it for the average punter betting $10 it would almost always be a in a situation where they fall into that 10% margin of error.
Even if there is an edge to the above average bloke (the best punters on here) it is likely to be fairly small, in the order of a few percent.
BetfairBetfair operates on a similar principle as above, but where the players are on both sides of the market and the house just takes the fee. This is even better for the bookie as he has absolutely no risk whatsoever if the odds are set incorrectly, that risk is borne by the player. the downside is it there needs to be a big player pool to lay bets, which doesnt happen easily. surprised there arent more bookies out there that operate in this maner.
PokerPoker is different to the rest (maybe it could be argued it is similar to betfair) in that you are playing against other people, and the house just takes a fee for hosting the game.
This is the area that i know the most on, but i wont bore people here unless they want to know more. But basically every hand vs any other hand has an expectation value, which for the best hand vs the worst hand is about 80%, but varies a ton obviously. This is the first form of luck.
the second form of luck comes from the fact that the game is an game of incomplete information, because the opponents cards are hidden. Each hand gets played out where players have to infer information about the other players hand. This leads a player to typically put another player on a range of cards, and how skilful a player is at this inference greatly affects the long term results.
said player has to be skilful enough to overcome the house fee (rake). Some players are good enough to do this, some arent. The rake also varies which further complicates it, as do general skill levels of opponents.
But in principle, players can win provided they can beat both the other players and the rake. this relies on the other players making enough mistakes. if everyone was of the same skill level it would be impossible to make money in a raked game.