Knowing ignorance is strength. Ignoring knowledge is sickness. But even planning can be overdone. Better stop short than fill to the brim. Over sharpen the blade, and the edge will be soon blunt.
Action is the key.
But the best of plans, when they are put into action, will most often encounter at least some obstacles along the way. And that's where flexibility enters into the process. The natural temptation in any quest for an objective is to use quick brute force to stubbornly overcome any obstacle that stands in the way. But Lao Tsu warns against it. For this would only cause resistance.