Analyzed 50+ trader CSVs over 30 days. Only ~15% had positive expectancy after fees + commissions across 30+ trades.

Spent the last 30 days analyzing trader CSVs to build a probability forecaster (passes / blows next prop firm account). The hardest finding to swallow:

Of 50+ traders who uploaded data with 30+ trades, only about 15% had positive expectancy after fees and commissions. Most of the rest had positive gross expectancy that flipped negative once costs were applied.

A few patterns worth sharing:

1. The 85% who had negative net expectancy fell into roughly two camps:

   - Camp A: gross win was real but commission drag killed it (high frequency / scalp strategies on micro contracts)

   - Camp B: gross win was already negative (bad strategy mistaken for variance)

2. The 15% with real edge had nothing in common stylistically. Some were trend followers, some mean-reversion, some discretionary. What they shared was structural: avg loss < avg win, and they sized down (not up) after losing days.

3. Most traders identify themselves as "variance unlucky" rather than "expectancy negative." The CSV math is unforgiving. 30 trades is enough to start telling them apart, 100 trades is enough to be confident.

4. Commission drag is consistently underestimated. A trader doing 200 round trips/month on MES at $0.50 each is paying $100/month before slippage. On a $1500 prop drawdown, that's ~7% of buffer per month just to participate.

Curious what the rest of you are seeing in your own logs. Specifically: when you backtested a strategy that worked but went negative live, was it usually fees, slippage, or behavioral drift?