The gamblers fallacy is thinking that because a team hasn't won or drawn in agaes "they are due a win". When you bet on a heavy underdog at say 5-1 the odds are broadly correct that you will win about every 6 games; but if the odds are slightly innaccurate and you make the same bet following certain criteria hundereds of times, you can grind out a 5-10% edge.
I lay odds on betting exchanges and make around 1000 bets per month in leagues all over the world.
