Rules loosening gradually through small exceptions, until the plan being followed is no longer the plan that was tested.
Drift happens one reasonable exception at a time. A slightly early entry, a stop moved a little for the spread, a setup taken on a lower timeframe because the day was quiet. Each is defensible and none is recorded as a breach.
The result is that the system producing your results is not the system you believe you are trading, so reviews diagnose the wrong thing. Traders in this state often conclude their edge has decayed when their adherence has.
Measure adherence explicitly. Score every trade as compliant or not against a written checklist, and track the percentage weekly. Drift is obvious in a number and invisible in memory. See plan-abandonment.
Original diagrams for the ideas on this page. Illustrative, not real market data.
How timeframes stack up. A daily candle is not different data, only coarser data: it opens where the first six-hour candle opened, closes where the last one closed, and its wicks reach the highest and lowest prices any of the four touched.
Educational only, not advice. Spotted an error? Post in Site Feedback.