Harry Potter and the Methods of Rationality

if that hadn't worked... even so, unless the Dementors had been instructed to Kiss anyone they found, failure shouldn't have been fatal.

This was different.

The Transfigured Muggle device could explode and kill them.

The interface between the technology and the magic could fail in any number of ways and kill them.

The Aurors could get in a lucky shot.

It was just, well...

Seriously dangerous.

Harry had caught his mind trying to argue itself into believing that it was safe.

And sure, the whole thing could work, but...

But even leaving out that rationalists weren't ever allowed to argue themselves into things, Harry knew he couldn't possibly have argued himself into estimating less than a 20% probability of dying.

Lose, said Hufflepuff.

Lose, said the voice of Professor Quirrell in his mind.

Lose, said his mental model of Hermione and Professor McGonagall and Professor Flitwick and Neville Longbottom and, well, basically everyone Harry knew except for Fred and George, who would have gone for it in a hot second.

He should just go find Dumbledore and turn himself in. He should, he really really should, it was the only sane thing to do at this point.

And if it'd been only Harry on the mission, only his own life that'd been at stake, he would have; he surely would have.

The part that was almost causing him to lose his concentration on the partial Transfiguration he was performing, the part that was threatening to open him to the Dementors...

...was Professor Quirrell, still unconscious, still a snake.

If Professor Quirrell went to Azkaban for his part in the escape, he would die. He probably wouldn't last even a week. He was that sensitive.

It was that simple.

If Harry lost here...

He lost Professor Quirrell.

Even though he's probably evil, said the Hufflepuff part of him quietly. Even so?

It wasn't a decision that Harry had made in any conscious way. He just couldn't do it. Losing was for House points, not people.

If you think your own life is valuable enough that you're not willing to take on an eighty percent probability of dying in order to protect all the prisoners in Azkaban, his Slytherin side observed, there's no way you can justify taking a twenty percent risk to your life to save Bellatrix and Professor Quirrell. The math doesn't add up, you can't be assigning consistent utilities over outcomes here.

The logical side of him noted that Slytherin had just won the argument.

Harry kept the Form in his mind, kept on casting the spell. He could always just abort the mission when he was done with the Transfiguration, he didn't want to lose the effort he'd already invested.

And then Harry thought of something else that suddenly made it very hard to keep the magic going, very hard to keep up his resistance to the Dementors.

What if the portkey doesn't take us where Professor Quirrell said it did?

It was obvious in retrospect the moment he thought about it.

Even if the planned escape went completely right, even if the Muggle device worked and didn't explode and didn't interact badly with the mated magic item, even if the Aurors didn't get in a lucky shot, even if Harry made it far enough away from Azkaban to use the portkey...

...there might not be a psychiatric healer at the end of it.

That was something Harry had believed when he'd trusted Professor Quirrell, and he'd forgotten to re-evaluate it after Professor Quirrell was no longer to be trusted.

You can't do this, said Hufflepuff. At this point we're talking mere stupidity.

Cold seemed to spread through the room, but Harry kept the Transfiguration going, even as his resistance against the Dementors faltered.

I can't lose Professor Quirrell.

He tried to kill a police officer, said Hufflepuff. You already lost him, in that moment. Bellatrix is probably just what everyone thinks she is. Just take your Cloak back, go find Dumbledore and tell him you were tricked.

No, thought Harry desperately, not without talking to Professor Quirrell, there might be an explanation, I don't know, maybe he was standing far enough away from my Patronus that the Dementors got to him... I don't understand, it doesn't make sense on any hypothesis, why he would do that... I