It may once have made sense to devote so much time and effort to planning activities in advance. Today, planning is deployed most effectively as a way to avoid taking action. So long as the plan requires more detail and more discussion, we need not yet muster the courage to act.
Some planning is essential. The right amount is almost always less, especially when planning in advance. It is before the work begins that we know the least—about how to solve a problem, how long it might take, or what it might cost.
Strictly time-boxed to a day (or two at most), planning at the outset of a project helps us share the little we do know and calibrate a course together, however uncertain. But it is only when we act that our assumptions are tested, and we acquire new information. At that moment, the wise choice is to correct the course and act again.