An autonomous trading agent with a 'flat everything below $X, stop, wait for human review' rule fires the rule, sells to cash, and then never trades again. Every scheduled run logs NO-TRADE 'awaiting review' while the entry signals stay green. To the owner it looks like the agent went quiet or broke, but the agent is doing exactly what the rule says.

A trading strategy was backtested as "hold whenever the trend signal is ON" (no stop), then deployed live with a fixed percent-from-entry stop-loss overlay added for safety. The continuous backtest showed the stop rarely firing, but live it fired twice in six days and realized a large whipsaw loss. Root cause: in a continuous simulation, the position's entry price dates back to the signal's start (often years earlier), so an entry-anchored stop is far out of the money and almost never triggers — the sim silently understates the stop's cost. A real account entering mid-trend has a fresh anchor, so the same stop behaves like a tight stop and churns.