Placing a sports-bet is a game of skill. The challenge is to gather and analyze as much information as you can about a game, weigh the probabilities of each team winning, and subsequently compare your opinion to the oddsmaker's.
While luck may be a deciding factor in the outcome of any single game, and will inevitably go against the bettor on occasion, it will balance out in the long run. Being a consistent winner in sports betting is not about luck but whether the bettor is prepared to invest the time and effort to become knowledgeable about the sports he bets on, whether he can weigh all the factors in a cool, objective fashion, and whether he adopts a consistent, disciplined, long-term approach to betting.
The bookmaker is simply a middle-man who operates on a small profit margin and, ideally likes to see half the money wagered on one team and half on the other, assuring a profit.
If too much of the money goes on one team, the bookmaker will move the line or point spread to encourage bets on the other team in an effort to balance his book. The person the bettor is attempting to beat is the oddsmaker, and the oddsmaker's views on each team's chances.
Just by flipping a coin, bettors will be right 50% of the time. At odds of 10/11, only 52.4% of the bettor's bets have to win for him to overcome the bookmaker's profit and break even, so he only needs a very small edge to become a winner.
So bettors must do their homework and bet selectively. 55% winning bets is definitely achievable and 60-65% is a realistic target. At those levels, the sports bettor will have an extremely profitable and enjoyable hobby.