It was overheard on Twitter
"Don't fall in love with your plan, it is almost certainly wrong "
A plan is a strategy for success. Strategies are hypothesise . Hypothesise need tests to verify - just like you learned in High School science class. That test is the Measures of Effectiveness and Measures of Performance of the outcomes from your project as well as the Technical Performance Measures that are used to take corrective actions needed to reach the goal of delivering value in exchgange for time and money.
The Plan describes where we are going, the various paths we can take to reach our destination, and the progress or performance assessment points along the way to assure we are on the right path.
These assessment points measures the “maturity” of the product or service against the planned maturity. This is the only real measure of progress – not the passage of time or consumption of money.
Wrong in the planning sense can only be wrong if you are managing your project Open Loop with no assessment of Effectiveness, Performance, Risk reduction, cost absorption, time performance or all the ...ilities associated with spending other peoples money.
So it is true that the Plan is wrong if you're not managing in the presence of uncertainty, feedback, and taking corrective action.