The “strategy as addition” mentality is persistent, despite it’s lack of effectiveness. It persists because the reality of strategy is much harder to engage with. At its core, strategy is about choice. Strategic planning is about looking at trends in the environment, as well as past results, and making deliberate choices about what activities to begin, what activities to continue, and what activities must be ceased.
These choices are hard to make. No one wants to stare down a fork in the road at two unknown paths and be forced to choose. No one wants to be the one blamed for making the wrong choice.