As the saying went, "There is no battle you will lose if you know yourself and your enemies well."
The outcome of the battle did not depend solely on the strength of the army on both sides; it was also a battle of intelligence information collected about each other.
Why were the strategists of old so well respected? The crux laid there. A good strategist could accurately plot against an enemy, even with little information, thereby gaining an upper hand. They were sure to win.
From Jiang Pengji's point of view, those people not only had exceptionally intelligent brains, but they could accurately diagnose the situation at hand and re-enact it well. It was shocking. When the people just started to see the beginning, their brains had already predicted the ending. That was the difference between an average person and a strategist.