As the saying goes, "the house always wins." In the case, the house will almost always win because the odds of a particular wagering proposition are lower than they should be.
When low odds are listed for a given contest, it favors the house because the amount required to be wagered is high and the return is low. Sportsbooks and bookmakers are sometimes forced into putting these lines out there because the game is evenly matched, there is a lot of action coming in, or some other outside pressure is pushing the lines down (such as lots of action in Las Vegas). Since the odds favor the house, bookmakers will never shy away from placing an underlay on the board, but try not to do it often. Players like to win and in order to do so, need reasonable odds. If a bookie consistently posts underlay odds, they will not attract enough bets.