Ceiling deterioration changes the flight before it violates rules
Lowering ceilings often degrade decision quality while still remaining legal. The pilot adapts by descending, choosing "the least bad" layer, and continuing forward. This adaptation can feel like competent decision-making because the aircraft remains clear of clouds. The problem is that the plan is no longer stable. Each adjustment is a signal that the mission is changing, but pilots often treat it as temporary turbulence in the plan. The danger is not legality. The danger is that the flight has shifted from executing a plan to managing a deteriorating situation.