Grant's genius was being not being deterred by casualties, rather than being willing to take them. It's a minor distinction, but a distinction nonetheless. Take for example the Battle of the Wilderness. It was his first face to face meeting with the ANV. In that battle both sides took heavy casualties, with the South probably gaining a small tactical victory, at worst, it was a draw. Prior to Grant, in the East, no matter who the commander was, the AoP would have headed back to Washington, tail tucked between it's legs. The morning after this battle though, the Confederates could hear the Union bands playing and realized they were moving South, via a flanking manuever, rather than north, as had always been the case in the past. Grant wasn't stupid, he knew continued fighting would net little, but he also knew that the North had the manpower to easily absorb the casualties, and that the South did not. Such a simple idea, but one hard to grasp in the face of setback after setback. Even in victory, the Union generals in the East prior to Grant couldn't seem to grasp that simple equation. For example, victories at Antietum and Getteysburg netted the north little, because of the unwillingness of the Northern generals to follow up despite a badly maimed foe and vastly superior numbers, including large numbers of men who had seen little or no fighting. Grant changed the equation, and it was his persistance that ultimately doomed the Confederacy (with some help from the equally persistant Sherman). By 1863, the Union had almost equalled the South in the quality of it's troops. But it took a year for it to equal it in the quality of their leaders (at least in the East).
