The first plan should survive being questioned by the position that actually develops.

A plan made at the start is a guess made with the least information you will ever have. Holding it loosely is not weakness; the situation in front of you now contains facts that were not available then, and those facts have a right to argue with the original idea. What usually goes wrong is not bad planning but loyalty to a plan after it has been overtaken.

Set a point in advance where you will reread your own plan against what has happened. Ask what you would decide if you were arriving today with no history. Then keep, adjust, or drop it on purpose.