In the Battle of Stalingrad in 1942, the German army suffered heavy casualties. So in order to save the situation, Hitler reorganized Army Group South and appointed Manstein as commander, hoping that Manstein would be able to make a surprise plan to save the German army's disadvantage on the Soviet battlefield and regain the initiative.
After Manstein's research, he proposed two military plans to Hitler, the first of which was that the Germans voluntarily abandoned their defense lines on the Donez and Mies rivers, lured the Soviet army into the lower reaches of the Don River, and surrounded the Soviet army. The second suggestion was to launch an offensive before the Soviets could replenish their winter losses, inflicting heavy losses on the Soviets. Hitler weighed it up and chose the first option, and designated the battle code as "Fortress". In fact, both of Manstein's plans were good, and Hitler would achieve good results no matter which one he chose to implement.
However, this very good opportunity to reverse the tide of the war was eventually squandered by Hitler. When the fortress operation was ready to be carried out, Manstein advised Hitler that he hoped to set the attack in May, so that the Soviet army could be caught off guard and win more. Unfortunately, for various reasons, Hitler did not attack the Soviets until July 5. After two months of repairs, the Soviet army has built fortifications, the troops have been assembled, and everything is ready for war. The German superiority over the Soviets was gone.
But even so, the Germans still defeated the Soviets in the face of more soviet troops than themselves, and at the beginning of the Battle of Kursk, the Germans had a firm advantage, but with the Soviet counterattack and the Allied landings in Sicily, Italy was beaten to a screeching escape. On the one hand, Hitler did not see the hope of victory in Kursk on the one hand, so he ordered the transfer of troops from the Eastern Front to support the Western Front, and the Battle of Kursk was over. It is conceivable that if Hitler had seized the time at the beginning and launched an offensive before the Soviets were ready, then perhaps the Germans would have won a little more, and it would not have been impossible to regain the initiative in the war.