I believe that in the longrun you will almost certainly make a profit, or at least not a loss. The risky thing is this combination ;
1) Someone wins big AND someone invests BIG before you regain your loss. Then your percentage will get much lower and it will be very hard to make money backk
i agree, there was a chart about one of these gambling casinos which showed their profit over time (i will add it later here if i find the chart again) but anyways it showed dips in the profitability of the casino which indicated a big loss by the casino (big win by the players) but eventually it came back to normal although it takes a longer time if the dip is big too but in the long run it will become profitable again.