Software engineering, for all its faults as a field, figured this out a long time ago. The essence of agile (the good parts) is: the people doing the work understand it best, and the plan is wrong (and making the plan is a waste of time).
Most implementations of Agile that I've seen do keep the plan, but the plan is allowed and even encouraged to change. High level planning still provides valuable insight, especially from a business perspective which is the whole point of the majority of systems.
Most implementations of Agile that I've seen do keep the plan, but the plan is allowed and even encouraged to change. High level planning still provides valuable insight, especially from a business perspective which is the whole point of the majority of systems.