Eliezer Yudkowsky - Harry Potter and the Methods of Rationality

They both heard the voice, like a long-dead corpse had spoken words and those words themselves had aged and died.

The Dementor's speech hurt their ears as it said, "Bellatrix Black is out of her cell."

There was a split second of horrified silence, and then Li tore out of his chair, heading for the communicator to call in reinforcements from the Ministry, even as McCusker grabbed his mirror and started frantically trying to raise the three Aurors who'd gone on patrol.

In a scarred and ruined corridor, lit by dim gas lights, a boy slowly crept forward, one hand stretched out, toward the unmoving snake that was the body of his teacher.

Harry was only a meter away from the snake's body when he first felt it, tickling at the edge of his perception.

Ever so weakly, a sense of doom...

Professor Quirrell was alive, then.

The thought engendered no feeling of joy, only a sort of empty despair.

Harry would still be caught soon, and no matter how he tried to explain, it still wouldn't look good. No one would trust him again, they would think he was the next Dark Lord, they wouldn't help him when it came time to fight Lord Voldemort, Hermione would give up on him, probably even Dumbledore would look for another hero...

...maybe they'd just send him home to his parents.

He had failed.

Harry looked at the crumpled body of the police officer he'd stunned, the already-drying blood from the minor cuts and slashes, the burned places on the intricately embroidered red robes.

He'd been stupid. He shouldn't have stunned the police officer, should have just stayed with his original story about being kidnapped by Professor Quirrell...

It might not be too late, whispered a voice inside him. You might still be able to fix your mistake. The Auror saw you, he remembers that you stunned him... but if he were dead, if Professor Quirrell were dead, if Bellatrix were dead, there would be no one to contradict your story.

Slowly, Harry's hand started to rise, pointing his wand at the police officer and -

Harry's hand halted.

He had a distant sense he was behaving uncharacteristically of himself, somehow. Like there was something he'd forgotten, something important, but he was having trouble remembering what it was, exactly.

Oh. That was right. He was someone who believed in the value of human life.

A sense of puzzlement accompanied the thought, he couldn't quite remember why other people's lives had seemed valuable...

All right, said the logical part of him, w hy has my mind changed between then and now?

Because he was in Azkaban...

And he'd forgotten to recast the Patronus Charm...

Doing anything at all, somehow, seemed like a tremendous effort, like the thought of action itself was a weight too heavy to lift; but it did seem like a good idea to recast the Patronus Charm, for he was still able to be afraid of Dementors. And though he couldn't remember what it was like to be happy, he knew that this wasn't it.

Harry's hand rose to hold his wand level before him, his fingers took the starting positions.

And then Harry paused.

He couldn't... quite remember... what he'd used as his happy thought.

That was odd, it had been something very important, he really ought to be able to remember it... something to do with death? But that wasn't happy...

His body was shivering, Azkaban hadn't seemed so cold before, and it seemed to be getting colder even as he thought. It was too late for him, he'd already sunk too far, he'd never be able to cast the Patronus Charm now -

That may be the Dementation talking rather than an accurate estimate, observed the logical part of himself, habits that had been encoded into sheer reflex, requiring no energy to activate. Think of the Dementors' fear as a cognitive bias, and try to overcome it the way you would overcome any other cognitive bias. Your hopeless feelings may not indicate that the situation is actually hopeless. It may only indicate that you are in the presence of Dementors. All negative emotions and pessimistic estimates must now be considered suspect, fallacious until proven valid.

(If you'd been watching the boy as he thought, you would have seen a distant, abstract, puzzled frown move across his face, below the glasses and the lightning-bolt scar. His hand stayed in the starting position for the Patronus Charm, and did not move.)

The presence of Dementors interferes with the part of you that processes happiness. If you cannot retrieve your happy thought by mnemonic association on the key of happiness, perhaps you can get at the memory some other way instead. When was the last time you talked to someone about the Patronus Charm?

Harry couldn't seem to remember that either.

A crushing wave of despair swept over him, and was dismissed by the logical part of himself as untrustworthy, external, not-Harry, the dull weight still pressed him down but his mind went on thinking, it didn't take much effort to think...

When was the last time you talked to someone about Dementors?

Professor Quirrell had said that he was already able to feel the presence of Dementors, and Harry had said to Professor Quirrell... he'd told Professor Quirrell...

...to hold to the memory of the stars, of falling bodilessly through space, like an Occlumency barrier across his entire mind.

His second Defense class of the year, on Friday, that was when Professor Quirrell had shown him the stars, and again on Christmas.

It didn't take much effort to remember them, the searing points of white against perfect blackness.

Harry remembered the great cloudy wash of the Milky Way.

Harry remembered the peace.

Some of the coldness at the fringes of his limbs seemed to retreat.

There were words he had spoken out loud on the day he'd first cast the Patronus Charm, his mind could remember the sounds and the speech even as the feelings seemed distant...

... I thought of my absolute rejection of death as the natural order.

You cast the True Patronus Charm by thinking about the value of human life.

...But there are other lives that are still alive to be fought for. Your life, and my life, and Hermione Granger's life, all the lives of Earth, and all the lives beyond, to be defended and protected.

Then the idea of killing everyone... that hadn't been his true self, that had been the Dementation talking...

Despair was the Dementors' influence.

Where there's life, there's hope. The Auror is still alive. Professor Quirrell is still alive. Bellatrix is still alive. I'm still alive. No one's actually died yet...

Harry could picture the Earth, now, in the midst of the starfield, the blue-white orb.

...and I won't let them!

"Expecto Patronum!"

The words came out a little halting, and when the human shape burst back into existence it was dim at first, moonlight instead of sunlight, white instead of silver.

But it strengthened, slowly, as Harry breathed in deliberate rhythm, recovering. Letting the light drive back the darkness from his mind. Remembering the things that he had almost forgotten, and channeling them back into the Patronus Charm.

Even when the light blazed full and silver once more, illuminating the corridor more brightly than the gas lamps, banishing fully the cold, Harry's limbs still shook. That had been too close.

Harry took a deep breath. All right. It was time to reconsider the situation now that his thoughts were no longer being artificially darkened by Dementors.

Harry reviewed the situation.

...still looked pretty hopeless, actually.