American Military History, Volume 1 by Richard W. Stewart

It seemed as if at this point in the battle Hooker simply lost his courage. Since he did not know exactly where Lee was, he began taking counsel of his fears and failed to follow his own plan. Over the vehement protests of his corps commanders, he ordered the troops back into defensive positions around Chancellorsville, surrendering the initiative to Lee. The Federals established a line in the forest, felled trees for an abatis, and constructed earth-and-log breastworks. Their position faced generally east and south, anchored on the Rappahannock on the east; but in the west along the Orange turnpike, it was weak, unsupported, and hanging in the air. Lee brought his main body up and on May 1 made contact with Hooker's strong left.

At the same time, Stuart's cavalry discovered Hooker's vulnerable right flank and promptly reported the intelligence to Lee. Conferring that night with Lt. Gen. Thomas "Stonewall" Jackson, Lee made a truly daring decision. Facing an army much greater than his own, having already divided his forces by leaving some units back at Fredericksburg, he decided to divide his forces again to further envelop the envelopers. Accordingly, Lee committed 17,000 men against Hooker's left to hold it in place while Jackson with 26,000 men made a wide, fifteen-mile swing to get beyond Hooker's right flank. Lee's decision was technically a violation of the principles of mass and concentration; but the principles are guides, not laws. A bold commander can knowingly undertake a higher measure of calculated risk if the potential reward is high enough. And Lee was probably the boldest risk taker of the war. In addition, while Lee's two forces were separated, their common objective was the Army of the Potomac and their ultimate routes converged on a common center.