Eliezer Yudkowsky - Harry Potter and the Methods of Rationality

Professor Sprout and the form of Susan Bones were dueling in flashes of light and leaves; and the blazing green of a Greater Drill Hex erupted from midair and chewed halfway through the outer layer of Professor Sprout’s shields. The Herbology Professor turned and fired a broad wash of yellow at where the Drill Hex had come from, but the spell didn’t seem to hit anything.

Yellow blazes, blue facets, dark green plant-tendrils and swirling purple flower petals…

It was when Professor Sprout started firing arcs of crimson in all directions that one of the crimson blades caught something in midair, the Invisibility Cloak not concealing how the crimson arc was absorbed and winked out; and Lesath’s presence beneath the Invisibility Cloak fell to the ground.

And that gave not-Susan-Bones time enough to stand still, catch her breath, and scream something that inspired in Harry another surge of dread; and the white spark that blazed out went through Professor Sprout’s chewed shields and her plant-armor and dropped her.

Not-Susan-Bones went to her knees, panting, her robes soaked in sweat.

Her head turned to look around her, at the bodies lying stunned on the floor or wrapped in vines.

“What,” said not-Susan. “What. What. What. ”

There was no reply. The victims entangled in Professor Sprout’s vines weren’t moving, though they did seem to be breathing.

“Malfoy…” said the pink-haired form of Susan, still gasping for breath.

“Draco Malfoy, where are you? Are you there? Call the Aurors already! Merlin damn it— Homenum Revelio! ”

And Harry found himself visible again, staring in his mirror at the form of Draco Malfoy half-visible beneath a shimmering cloak, standing behind not-Susan, pointing his wand at a gap in not-Susan’s blue haze.

Harry’s mind moved in flashes of insight, too slow and yet too fast; even as Harry’s mouth opened and he inhaled in preparation to shout. beware the constellation

there was a constellation named Draco

if you could control a Professor you could control a student

“ Duck! ”Harry shouted, but it was too late, a bolt of red light caught the back of not-Susan’s head at point-blank, smashing her to the floor.

Harry stepped around the corner and said, “ Somnium Somnium Somnium Somnium Somnium Somnium. ”

Draco Malfoy’s shimmering form collapsed in a heap.

Harry took a moment to catch his breath. Then Harry said “ Stupefy! ” and verified that, yes, the Stunning Hex did hit Draco Malfoy’s form.

(You could be mistaken about whether a Somnium had really hit. Harry had seen enough horror movies, not to mention the business with the Sunshine Regiment, that he wasn’t about to make that error again.)

After a further reflection on this, Harry cast another Stunning Hex into the prostrate form of Professor Sprout.

Harry gripped his wand, staring at the scene, breathing heavily from the exhaustion. He didn’t have enough magic left to cast a messenger Patronus to Dumbledore and he really really should have thought of that possibility immediately this time around. Harry started to reach back to where his mirror had fallen, to see if it was now unjammed.

And then Harry hesitated.

His note to himself had said to avoid notice from Aurors, and Harry still did not know what was going on.

The crumpled form of Professor Quirrell gave another series of racking coughs, reached out a hand to the wall beside him, and slowly pulled himself to his feet.

“Harry,” croaked Professor Quirrell. “Harry. Are you there?”

It was the first time Professor Quirrell had ever called him by his first name.

“I’m here,” Harry said. Without any conscious thought, his feet were moving forward.

“Please,” said Professor Quirrell. “Please, I haven’t… much time.

Please take me… to the mirror… help me… get the Stone.”

“The Philosopher’s Stone?” Harry said. He glanced around at the scattered bodies, but he couldn’t see Draco anymore, the revealment had worn off. “You think Mr. Nott was right? I don’t think Dumbledore would—”

“Not—Dumbledore,” gasped Professor Quirrell. “Because—Sprout—”

“I understand,” Harry said. If Dumbledore had been the one behind it all, he wouldn’t have needed to mind-control a Professor in order to use Memory Charms.

“Mirror… ancient relic… could hide anything… Stone could be there… many others want Stone… one sent Sprout…”

Harry repeated rapidly, “The mirror down there is an ancient relic that can be used to hide things, and it would be one possible place to hide the Philosopher’s Stone. If the Philosopher’s Stone is inside the mirror then any number of people might want to get it. One of them is controlling Sprout and that would explain what their goal really is… only… that doesn’t explain why Sprout’s controller would go after Hermione?”

“Harry, please,” Professor Quirrell said. His breathing was yet more labored now, his voice came with excruciating slowness. “It’s the one thing… that can save my life… and I find, now… I don’t want to die… please, help me…”

And somehow that tore it.

Somehow that was a little too much.

The sense of detachment that had come over Harry when Professor

Sprout had arrived, the broken suspension of disbelief, was returning; his Inner Critic weighing up everything as though it were a set-piece. Timing, probability, so many people showing up at the same door, the Defense Professor’s desperation… this whole situation didn’t feel real. But he might be able to solve it if he just took time to think things through in advance, instead of running off at adventure’s first call. All the accumulated experience from the last year had finally crystallized into something like a touch of battle hardening. An instinct born of past disaster was telling Harry that if he just rushed on ahead, he would end up afterward in a sad conversation, realizing that he’d been stupid. Again.

“Let me think,” Harry said. “Let me think for a minute before we go.” He turned away from the Defense Professor, looking at the unconscious bodies draped in various shapes over the floor. There’d been so many puzzle pieces already, this last year, maybe everything would just fall into place with one more piece…

“Harry…” the Defense Professor said in a faltering voice. “Harry, I’m dying…”

One more minute can’t make the difference he’s had the WHOLE YEAR to be sick it’s IMPROBABLE that his life versus death would be precisely timed to rest

on this last minute no matter what happened to Hermione— “I know! ” Harry said. “I’ll think quickly! ”

Harry stared at the bodies and tried to think. There was no time for doubts, for caveats, no brakes or second-guessing just take the first thoughts and run with them—

In the back of Harry’s mind, fragments of abstract thought flitted past, heuristics of problem-solving that there was no time to rehearse in words. In wordless flashes they shot past, to set up the object-level problem.

— what do I notice I am confused by—

—the first place to look for a problem is whatever aspect of the situation seems most improbable—

—simple explanations are more probable, eliminate separate improbabilities that must be postulated—

Professor Snape had already been here then Professor Quirrell had arrived then Harry had arrived (via Time-Turner) then the adventuring party had arrived and Draco had been revealed (part of the party) then Professor Sprout had shown up.