He was PISSED when his 6th army surrendered at Stalingrad. He expected them to fight to the last bullet, whether that be firing on Russians or ending their own lives (he specifically listed suicide as acceptable). The surrender undermined the narrative he wanted to tell the German people that the 6th army viewed the German struggle as more noble than their own lives. Instead they "proved" to Hitler that they were cowards who would surrender to an inferior race.