Assuming that there is no spread and no slippage, an adequately long series of random trades, i.e buy 1 lot at today, sell one lot tomorrow, buy one lot the next day, will result in 0 change and a 50%/50% win/loss ratio. Correct?

If so, I can employ a stoploss that cuts some of that loss. So my average win is higher than my average loss. In a perfect world, that should profit.

However, there is spread and slippage in the real world. I've backtracked forex chart histories for the last 5 years, and on my excel sheet calculator, I seem to be able to profit even with double the slippage (I considered 4pips for the EURUSD instead of 2pips). I have it essentially buy at midnight, sell the next midnight, buy the midnight after that, etc. My entering amount is 4% of my account balance and the stoploss is set at 2%. So with a $10,000 balance, I enter with $400. If it ever goes below -$200, the stoploss triggers and exits the trade, then waits for midnight.

I am not accounting for the possibility where the trade seems to profit based on two data points spaced a day apart, yet in actuality dips below that sometime during the day and triggers the stop loss, marking a loss instead of a profit. I feel that I have made up for that by doubling the slippage. If this is truly a big deal, I can add intraday data points and modify my macro to calculate it.

If it seems too easy and good to be true, it definitely is. But what's wrong with my reasoning?