Wellington's quip about having won Waterloo illustrates a problem with hindsight. If a commander knew in advance where and when Napoleon would attack or when Blücher would arrive, he would deploy differently. Napoleon would then respond to the new deployment, producing a different battle from the one that supplied the hindsight. Counterfactual analysis must therefore model reactions and feedback instead of changing one decision while freezing every other actor.
Notable Point · 1:09:56-1:10:31
Why hindsight would create a different Battle of Waterloo
Knowing Napoleon's attack plan or Blücher's arrival time would change both Wellington's deployment and the opponent's response, not simply improve the historical result.