Why plan? So much changes, so many things are unforeseen. The world is unpredictable and out of our control. The people we depend upon are fallible and have free will. There is no telling what they will do, how they will react to us.
Any airliner spends most of each trip off course and pointed in the wrong direction. Wind, weather, and traffic are constantly diverting the vessel from the perfect path. Rather than being discouraged by the impossibility of staying on course, the pilot and the instruments are continually working to compensate for these random and unforeseeable influences. After a trip of “unplanned” but expected diversions, airliners almost always arrive at their intended destinations. What would be the result if the pilot did not declare where and when he would land? How would he react to the distractions and diversions? Would you buy a ticket on that plane? Rather, could that pilot enroll you in his project?
You have many choices each day–even if they don’t seem like choices–and a consistent target will give you a ready reference for making those choices. Your plan is useful not because it is a description of what will happen, but because it provides a reference point to evaluate and respond to the inevitable circumstances that differ from the plan.
Planning is not Predicting.
The value of a plan is not as a guarantee that things will happen exactly as you expected, but that when the unexpected does -inevitably- occur, you can notice and respond to the deviation.