If we don't know which port we're steering for; no wind is favorable - Seneca
This is the primary reason for planning and plans. Without a plan, we can't know what done looks like in any measure meaningful to the decision makers. Of course, Plans must change when the winds change. Any sailor knows that.
Planning and plans produce strategies. Strategies are hypotheses. Hypotheses require experiments to test their validity. These tests are the feedback from the Measures of Effectiveness, Measures of Performance, Technical Performance Measures, and Key Performance Parameters of the project compared to the planned MOE, MOP, KPP, and TPM's.
When these are not going according to plan, corrective or preventive actions are needed to get back on course, just as the Seneca's sailor would do.