Michael Porter compressed strategy into a single move: the essence of strategy is choosing what not to do. A plan to be good at everything, for everyone, is the most reliable sign of having no strategy at all — it makes no choice, and therefore commits no resources to the point where the outcome is actually decided.
The refusal is what makes a strategy checkable. "Become the market leader" declines nothing and so predicts nothing; concentrate on this segment, decline the adjacent ones that would dilute the effort, expand only once the position is secure contains a judgment about where advantage lies, a decision about where to commit, and an order in which to act. The declined options are not oversights — they are the strategy, stated negatively. This is also where strategy leans on judgment: knowing what is worth doing is inseparable from knowing what is not, and no amount of data will make the refusal for you.
See also: Policy, Strategy, and Tactics, The Strategy Kernel, Mistaking Activity for Direction.