The only good idea for the Confederates that day was to withdraw from this accidental battlefield so favourable for the Union, and resume a Fabian strategy of living off the Pennsylvania country side. Never mind the consequences of a defeat, the Confederates couldn't afford the casualties required for a victory.
In What is Operational Art?, Major Walter E. Piatt makes the point that much of early 19th century military theory was a severely wrong interpretation of Napoleonic warfare:
All the lessons of Napoleon may not have been fully embraced by historians and
theorists. The wrong lesson may have been learned by the great military leaders that followed. This wrong lesson, or misconception of Napoleon, is that a war could be decided by a single battle. This misconception created a singular vision towards military operations and would influence military instruction in the nineteenth century. This singular vision, or desire to end the war with a single decisive battle, may still linger in the minds of present day officers and hinder understanding of operational art.
Epstein proves that this is clearly the wrong lesson to derive from the study of Napoleon. It may have been this wrong lesson though, that planted the desire for many leaders to emulate Napoleon. After Napoleon military leaders desired to obtain the one quick decisive battle to end the war. It was not to be.
It would take another genius a half a century later to figure it out, his name was Ulysses S. Grant.
Lee's entire Pennsylvania campaign was predicated on the notion that the Army of the Potomac could be destroyed in a single massive battle, a Pennsylvania Cannae if you will. And that if this battle was fought to a successful conclusion, any number of Confederate casualties was acceptable for such a victory. But this was no more possible for Lee in 1863 than it was for Grant in 1864-5. Only a long series of battles could destroy either the Army of the Potomac or of Northern Virginia because, just as for Napoleon's Grande Armee in 1813-4:
Through the sheer size of Napoleon's army and the use of distributed maneuver it would require more than one battle to destroy his army. Distributed maneuver also forced Napoleon to plan for several engagements in a single campaign. [ibid]
If Lee had truly understood these lessons from a half century earlier, he would have heeded Longstreet's advice for the second day at Gettysburg:
Can't we just sit for once, and let the damn Yanks come at us instead.
It was, after all, in the disastrous charge by Pickett the next day where nearly half of all Confederate casualties for the battle were incurred. The truly awesome defensive capability of a modern army, that would be exposed to the entire world in 1915 at Verdun, was already evident, for those willing to see, on the Round Tops and Cemetery Ridge in that first week of July, 1863.
Lee, on July 2 and 3 1863, choose to accept any number of Confederate casualties for the pipedream of winning the Civil War in a single battle. Ironically, the consequent destruction of his army's offensive capability ended all hope for a negotiated settlement with the North. Like the Japanese commander at Midway eight decades later, Lee was the only commander on the field who could lose the war in an afternoon.