My general philosophy of decision-making de-emphasizes the planning/execution distinction. But I am not an agility purist. Nobody is. You can think of the Agility Purist archetype as a useful abstraction. This mythical kind of decision-maker believes that a mind and personality that is sufficiently prepared for a particular domain (say programming or war or biochemistry) needs no preparation for specific situations or contingencies. This magical being can jump into any active situation in that particular domain and immediately start acting effectively.
At the other extreme you have an equally mythical Planning Purist archetype who has thought through every possible contingency all the way through the end and can basically hit “Start” and reach a successful outcome without further thinking. In fiction, this is best represented by jewelry heist capers based on long, involved and improbably robust sequences of moves, as in Ocean’s Eleven or The Italian Job. A few token things go wrong, but overall, these narratives play out like Rube Goldberg machines.
Clearly, reality lives somewhere in the middle. But planning vs. execution is not always a good pair of trade-off variables to create reality out of these two asymptotic myths. That distinction only works when there are a lot of known, hard temporal constraints or formal logical constraints (socks before shoes) in play. These actually help simplify things and make planning/execution a useful model.
When there is none of this temporal structure (what David Allen calls “a hard landscape”) and everything is rather fluid and chaotic, I find it useful to think in terms of a different distinction: positioning moves vs. melee moves. I learned of this distinction from Alfred Thayer Mahan’s The Influence of Sea Power Upon History. Here’s a brief primer.