So to explain how some wizards draw absurd amounts of power, the Paranet Papers added something called Mental Toughness, which basically makes a character into more of a calm mental fortress.
…Except that every Mental Toughness has a Catch that ‘breaks’ it. A hole in their armor. Anything that breaks their self-image or their convictions and briefly makes them unable to entertain that kind of dispassion.
McCoy’s Catch? People fucking with his family.