The problems that appear after the strategy works
Early failure is loud: over-sizing, no stops, no plan. Late failure is quiet, and it happens to traders who have already solved those things.
The pattern is consistent. A trader builds something profitable, runs it well for a period, and then finds ways to prevent it working. Naming these in advance is most of the defence.
Sabotage one: succeeding, then changing everything
Three profitable months. The trader concludes they have understood the market and begins improving: a new indicator, a second instrument, a shorter timeframe, larger size.
Every change is individually reasonable. Together they replace a tested system with an untested one, and the track record that justified the confidence was produced by the system that no longer exists.
The rule that prevents it: changes go in a queue with a date. Nothing is implemented mid-quarter. When the date arrives, one change is made and measured for 50 trades before the next.
Sabotage two: the size ratchet
Confidence grows, so size grows. Rarely as a decision — usually as drift. 1% becomes 1.3%, then 2%, then "this one is obvious, 4%."