...as soon as the first shot is fired. However, the art of planning is invaluable. In other words, plan for change and be ready to change your plans. Repeatedly. This be the foundation of an agile approach to solution development.
I agree with Ken Schwaber in that many agile methodologies do not feel very agile. Some major contenders are thinly veiled command-and-control frameworks in which you entrust your development effort. This kind of regimented approach is seen as a less risky flavour of agile for newcomers to the game. And it feels familiar to those who followed the phase-gate approach to development which was dominant in the last millenia.
Teams should spend focus and energy on meeting Sprint goals, as opposed to rigid adherence to, and maintenance of the process. And sure it’s easy for me to say. Over the past twenty years I’ve had the pleasure of working in dozens of teams, and most of them were comfortably small. Single-pizza sized. However, I have also clocked hours in larger projects and participated in dutiful loyalty to formally defined tasks and metrics gathering, all the while as velocity floundered. With few degrees of freedom to analyze and optimize the process itself, we lacked the tools to improve - at least during my residency.
What I am trying to impress on my fellow practitioners in the elusive art of agile solutioning is to keep the Agile Manifesto close to your hearts, regardless of the methodology your dev org follows. Strive for the three pillars of Scrum: transparency, inspection and adaption - of the product and the practice. It’s too easy to lose sight of the forest by focusing too much on individual shrubberies.