Ariana's death turns theory into consequence — Ariana's death turns theory into consequence

The confrontation involving Albus, Aberforth and Grindelwald ends with Ariana dead and the caster of the fatal spell uncertain. That uncertainty is the moral wound: Dumbledore cannot isolate guilt neatly.

His later caution, avoidance and service all grow from knowing that dazzling ideas did not protect the person most dependent on him.