Coupled with inferior Confed generals aside from Forrest. I know Lee made a lot of mistakes but he was a very motivational leader, which counts some. Jackson was asleep I guess during the Seven Days but otherwise he was unpredictable but often paired up with political generals on the other side.
The Nazis were a bit like the South, neither could afford any major mistakes. And mistakes are inevitable in warfare.
The overall strategy of the Southern States in the Civil War has never made sense to me. It was mentioned upthread that when the war began William Tecumseh Sherman was serving as the first superintendent of the Louisiana State Seminary of Learning and Military Academy which would eventually become LSU. This was his statement to a Professor who was a close friend and an enthusiastic secessionist:
"
You people of the South don't know what you are doing. This country will be drenched in blood, and God only knows how it will end. It is all folly, madness, a crime against civilization! You people speak so lightly of war; you don't know what you're talking about. War is a terrible thing! You mistake, too, the people of the North. They are a peaceable people but an earnest people, and they will fight, too. They are not going to let this country be destroyed without a mighty effort to save it... Besides, where are your men and appliances of war to contend against them? The North can make a steam engine, locomotive, or railway car; hardly a yard of cloth or pair of shoes can you make. You are rushing into war with one of the most powerful, ingeniously mechanical, and determined people on Earth—right at your doors. You are bound to fail. Only in your spirit and determination are you prepared for war. In all else you are totally unprepared, with a bad cause to start with. At first you will make headway, but as your limited resources begin to fail, shut out from the markets of Europe as you will be, your cause will begin to wane. If your people will but stop and think, they must see in the end that you will surely fail."
The Confederacy's situation in 1861 was somewhat similar to Japan's eighty years later in 1941. They had substantial military establishments at least comparable to the United States but a smaller population and productive capacity only a small fraction of the adversary they were facing.
At least Japan had the right idea. They knew that they had to act quickly and take as much territory from the US as possible before the US' massive advantage in productive capacity could be brought to bear. On a macro-strategic level the Southern States should have done the same thing. Their best chance was in 1861 and it was predetermined from the beginning that their chances would get worse in 1862, then get worse again in 1863, then get even worse in 1864, then continue to get worse in 1865 and beyond.
Gettysburg is, I think, a good example of this. Over the years many people have criticized Lee's decision to send Pickett, Pettigrew, and Trimble charging against the Union Line. Most of Lee's subordinates opposed the attack. Post war, General Longstreet claimed to have told General Lee that "I have been a soldier all my life. I have been with soldiers engaged in fights by couples, by squads, companies, regiments, divisions, and armies, and should know, as well as any one, what soldiers can do. It is my opinion that not fifteen thousand men ever arrayed for battle can take that position."
What became known to history as Pickett's Charge was tactically moronic. As an aside, Pickett himself hated that name because he was against the idea as well and, of course, it was a catastrophe. However, if you give Lee the benefit of the doubt, it may have been a sound strategic decision.
On a macro-strategic level, by 1863 the Union's massive advantage in productive capacity was having a major effect. I think Lee knew that July 3, 1863 was simply as good as it was going to get for his side. If Pickett's Charge had been successful and the Union Army had been thoroughly routed at Gettysburg there might have been a chance for the Southern States to secure a negotiated settlement particularly if they had followed up that victory by sacking Harrisburg (just 40 mi away and PA's capitol) or threatening Washington (~70 mi away) or Baltimore (~50 mi away).
Obviously Lee knew that his forces were weaker than the Union Army but I think he also knew that the disparity would be worse for him in 1864 and he simply decided that July 3, 1863 was likely to be a better day to try to win the war than any subsequent day would be.