This doesn't mean the plan was unnecessary...rather the plan carves out the neural pathways in your mind. The feeling part is important too since if I am so rigid then I am going to be crushed by the randomness of life.
I used to hear this a lot from one of my better bosses. I agree with it. It is, however, important to capture "planning". Any form is fine, whether scribbles or a list or a picture of a whiteboard. Trying to organize the raw info was usually a waste of time, but having it accessible as a reference wasn't.
They have a good lists of mind sweep / brain-dump triggers [1] that I think benefit everyone even without ever doing everything one writes down.
[1]: http://gettingthingsdone.com/wp-content/uploads/2014/10/Mind...
General George S. Patton, Jr.
No plan survives contact with the enemy.
Unknown
--Palindrome