The most-believed setup in retail trading. In training, the best RSI threshold returned +307 bps per trade — a money printer. Committed to that exact setting, tested once on unseen data: −45.6 bps, with a t-stat of −0.1. Every other "profitable" setting in the sweep was statistically indistinguishable from a coin flip. The edge was never there. It was the search finding the prettiest accident.
An order-flow momentum signal. Every one of the 8 best training combos was profitable in-sample (+8 to +10 bps) and every one inverted to a loss on unseen data (−7 to −9 bps). The edge didn't fade to noise — it flipped negative. Nothing cleared the cost bar out of sample.
Earlier versions backtested +224% and +233%. So we kept "improving" it — raising thresholds, adding a daily-bias multiplier, chasing the upward trend. The final optimized candidate lost −31.2%. The improvement was the overfitting tightening: every tweak fit the past more perfectly until the strategy had memorized noise. The bot was built and deployed before this was understood — and shut down before a customer ever paid for it.