Why do many EAs fail while the same strategy works perfectly in manual trading? - page 3

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Three reasons this happens consistently:

1. Execution latency
Manual trading has one advantage: you see the candle forming 
and decide when exactly to enter. An EA fires on a condition 
being met — but by the time the order reaches the broker, 
price has moved. On a 1-minute chart or during news, 
that gap matters. Manual trader adapts. EA doesn't.

2. Spread and slippage blindness
When you trade manually, you instinctively avoid entering 
during wide spreads. Most EAs don't have this filter built in 
unless you code it explicitly. Add a max spread parameter — 
if current spread exceeds X points, skip the trade. 
That alone eliminates a large chunk of bad fills.

3. Overfitting to historical conditions
The strategy "works" in manual trading because your brain 
filters setups in real time — you skip the ones that don't 
feel right. Backtests don't have that filter. The EA trades 
every signal the rules generate, including the ones you 
would have skipped manually.

Fix: walk-forward test on at least 6 months of out-of-sample 
data before going live. If performance degrades significantly 
on unseen data, the edge isn't real — it's curve-fitted.

The gap between manual and automated isn't the strategy. 
It's execution quality and parameter robustness.
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