Clausewitz called it Nebel des Krieges — the fog of war. Everything in war operates under uncertainty: where is the enemy, what are their intentions, what do they know about you.
The crucial insight: the fog is irreducible. You cannot wait for certainty because certainty never arrives. The competent commander acts on incomplete information while continuously updating as new information comes in.
This is ↗ @dave / bayes-as-updating applied to violence. Prior + evidence → posterior. The prior is your intelligence estimate. The evidence is what your scouts report. The posterior is your updated picture of the battlefield.