If you don't have an edge, you're basically 50/50, so even though you'll have volatility in the long run you won't be losing anything.
If you take an average price stock with decent volume, and make one round trip per day, with slippage and reasonable commissions (and yes there is slippage with non marketable lmt orders, cost of not getting filled) you are looking at about 0.06%
250 trading days in a year that is 15%.
If you do 2 round trips per day, that is 30% you have to overcome.

If you take an average price stock with decent volume, and make one round trip per day, with slippage and reasonable commissions (and yes there is slippage with non marketable lmt orders, cost of not getting filled) you are looking at about 0.06%
250 trading days in a year that is 15%.
If you do 2 round trips per day, that is 30% you have to overcome.

To the pros.