Question

Evan is charged with a crime. almost all federal courts and some state courts would not hold evan liable if, at the time of the offense, as a result of a mental disease or defect, evan lacked substantial capacity to

Answer 1

He lacked substantial capacity to appreciate the wrongfulness of his conduct or obey the law.
The brains of people who had mental defect or disease do not function the way normal people do. This might cause them to not fully understand the concept of Empathy or guilt that normal people do when we're seeing other people being hurt.