Due to prior victories at battlefield like Chancellorsville and Second Manassas, Lee’s confidence in his army went through the roof, thus causing him to forget that the confederate army consisted of only the common man, men who had never tasted the bloody, horrific sights of battle or even a military school for that matter. After larger scale wins for the South Lee began to treat his infantry as though they were invincible. Loosely giving orders to his lieutenants, who were then responsible for coming up with a designated plan themselves.
