The clip Asking Lupin for help from Harry Potter and the Prisoner of Azkaban (2004) with Daniel Radcliffe, David Thewlis
Is there no chance of fixing it?
Professor, why do the dementors affect me so?
I mean, more than everyone else?
Dementors are the foulest creatures to walk this earth.
They feed on every good feeling, every happy memory until a person is left with absolutely nothing but his worst experiences.
You are not weak, Harry.
Dementors affect you most because there are true horrors in your past.
Horrors your classmates can scarcely imagine.
You have nothing to be ashamed of.
I'm scared, professor.
I'd consider you a fool if you weren't.
I need to know how to fight them. You could teach me.
You made the one on the train go away.
There was only one that night.
But you made it go away.
I don't pretend to be an expert, Harry.
But as the dementors seem to have developed an interest in you perhaps I should teach you. But after the holidays.
For now, I need to rest.