No plan survives contact with the enemy (or reality), but that doesn't mean you can just wing it. Of course you need a specific plan, but you also need the ability to change that plan as needed, in a controlled and sensible way. Realising the problems of advanced planning means you need to spend more time, not less, on working out what you are trying to do.
I'm reminded of Eisenhower:
I tell this story to illustrate the truth of the statement I heard long ago in the Army: Plans are worthless, but planning is everything. There is a very great distinction because when you are planning for an emergency you must start with this one thing: the very definition of "emergency" is that it is unexpected, therefore it is not going to happen the way you are planning.
-- From a speech to the National Defense Executive Reserve Conference in Washington, D.C. (November 14, 1957) ; in Public Papers of the Presid...
Another month, another rationality quotes thread. The rules are: