Our goals can only be reached through a vehicle of a plan, in which we must fervently believe, and upon which we must vigorously act. There is no other route to success. - Stephen A. Brennan
The Plan is a strategy for the successful completion of our goal. A strategy is a hypothesis and a hypotheses requires that tests be performed to confirm we're on the right track. This is a fundamental missing concept in the management of projects. These tests must be feedback points at sufficiently small intervals to take corrective action to "stay on Plan," without disrupting the path to the goal.
This is the core paradigm for agile as well as Integrated Master Plan / Integrated Master Schedule. Both answer the question
How long are you willing to wait before you find out you are late?