It only took Lee one battle to figure it out. Unfortunately, it was Gettysburg, but that is war. Jackson could not be replaced, and the Army of Northern Virginia suffered from his loss the rest of the war.
Jackson could have motivated the Yankees to fight for the Confederacy! Cause if they didn't, they'd be on the receiving end of...
And therein lies the fear and dread the Yankees had for the Stonewall Brigade...