They never really touched on...

In the podcast they only speculated on it. They talked about his past and how he had this attitude of "not quitting until he could do it". They brought up football plays/moves, some of which he'd be completely and utterly incompetent at performing, while insisting on doing however many repetitions necessary to be able to perform them properly, even if it took him months. It's sorta what he did with those patients. He knew what he had to do on a theoretical level but he lacked the experience/ability to actually perform them... so he "practiced". The podcast also talked about his heavy drug use, which I assume contributed to whatever the fuck was wrong with this guy's head.

He sent out this creepy email to an employee of his in 2011. Sounds like he was fucked in the head for a long time and no one caught onto it.

https://www.dallasnews.com/news/crime/2015/08/25/7-chilling-thoughts-of-jailed-neurosurgeon-christopher-duntsch/

He seems to have what is called the God complex. You see him trying to succeed at different things. Once he was in medical school he thought he could do anything and fix anything. He seems to like the part of patients looking to him for help like he is a God. He tells them he will heal them. This power is in his hands during surgery.

As messing up surgeries I think he enjoyed crippling people just so they would look to him for more help. If he healed them they no longer needed him.