We spend the vast majority of our time helping new leaders create and implement 100-day action plans. Over the past decade or so, I can not think of a single instance in which a new leader actually followed the original plan he or she created.
Think Darwin. Survival of the fittest is survival of those best able to adapt.
Thus every 100-day action plan ever written was out of date the moment it was finished.
We don't work with leaders with a goal of helping them implement the 100-day action plan they started with. We work with leaders to help them and their teams deliver better results faster.
The plans are a starting point, not an ending point. The plans are important confidence builders. Having the plan puts the leader on the front foot in terms of confidence. Knowing the plan puts the team on the front foot in terms of confidence. Confident leaders and teams are better able to adjust along the way, using the plan as a baseline, starting point for what they do. Having the plan allows them to make conscious choices about how they are adjusting and how what they are doing is different than what they'd originally planned.
Plans are not made to be followed. Leaders are.