Cast that thought in terms of state. If all the state can be represented up front then plans are great. But if the understanding of the problem changes half way through a project and previously un-identified state is found during the runtime then a plan-execute pattern will get ugly quickly.

It is good to name things, but the challenge to manage isn't in the implementing of a plan-execute architecture. It is in identifying the threshold where there is enough runtime state in the problem domain that a plan-execute architecture can't be sustained.