My understanding is that "unbreakable" magic makes the object unable to change at macroscopic level, but doesn't prevent small alterations at microscopic level. And those small alterations at microscopic level, in case of a transfigured human, will lead to DNA damage and similar things. It's not known if the information encoded in the brain will resist or not - it's much higher level than DNA, so there is a good chance it would.
Another possibility if that "unbreakable" works fine on things that have very few moving parts, but if you try that on a human body then they become utterly incapable of changing. Their muscles don't flex, which means they can't breathe and their heart stops beating, and they die very quickly.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 109.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: