When we hear ...
"Don't fall in love with your plan, it is almost certainly wrong "
let's reflect on advice from IEEE Std 730-2014
Plan Management: It is obvious that the project must be managed during its execution, but perhaps not so obvious that the plan itself must be managed. Despite the fact that nearly continuous change destabilizes any plan, the plan itself must not be allowed to float and become meaningless. The project must adopt a discipline for monitoring, reviewing and revising plans that they are stable in application while responsive to change.
The management process of IEEE/ISO 12207-2008 requires the manager to control the execution of the project by monitoring and reporting progress, and investigating, analyzing and resolving problems that arise.
The common phrase used by many in agile is Plan-Do-Check-Act.
This starts with Plan. In order to Do, Check, and Act, we need a place to start. The Plan. So falling in love with our Plan and then not, Doing, Checking the outcome, and Acting on the progress to that Plan, determining the varaincies from that Plan, assessing the impact from those variances, would mean we are not managing the project.
This would also mean that falling in love with the Plan would require use ignorning the very basis of management in the presence of change.
So make plans, get feedback on the progress to plan, update the plan with this information, make a new or updated plan, schedule the work that the plan shows needed to be done, and measure progress to plan in units of measure meaningful to the decision makers.
Like the picture above, if you're going to embark on a day hike to Twin Sisters in Rocky Mountain National Park, you'd better have a plan. Not just for how long it's going to take, what your path is going to be, but have a Plan-B and likely a Plan-C when the weather goes bad, thunder storms come over the mountain, or any other disruptive event.
But most of all PLAN, and don't fall for that non-actionable statement that plans are almost certainly wrong. Because without the plan, you have no clue about what DONE looks like, how to get there, how long it will take, how much it will cost, or how you'll recognize DONE when it arrives.
Plans are Strategies for Success
They can be neither Right or Wrong, they can only represent you're current understanding of the emerging situation that leads to the current path to success.