Long long time ago, ancient state of Chu was planning a sudden military attack over the state of Song via a shortcut by crossing the River of Yong. To smooth the action, the military force marked the route for crossing the river in advance.
But what the army of Chu did not expect was that the water level raised significantly in a short period of time which the army did not notice; when the army marched on night following the marks, soldiers and horses were trapped in the deep water and more than 1,000 soldiers were killed. The attack action was called off.
Situation changes with time. Monitoring changes is a key element to successful implementation of plans.