“A part of the system that you cannot change” is a vague term (and it’s a vague term in the HPMOR quote as well). We think we know what it means, but then you can ask questions like “if there are ten things wrong with the system and you can change only one, but you get to pick which one, which ones count as a part of the system that you can’t change?”
Besides, I would say that the idea is just wrong. It is useful to assign fault to a part of the system that you cannot change, because you need to assign the proper amount of fault as well as just assigning fault, and assigning fault to the part that you can’t change affects the amounts that you assign to the parts that you can change.
“A part of the system that you cannot change” is a vague term (and it’s a vague term in the HPMOR quote as well). We think we know what it means, but then you can ask questions like “if there are ten things wrong with the system and you can change only one, but you get to pick which one, which ones count as a part of the system that you can’t change?”
Besides, I would say that the idea is just wrong. It is useful to assign fault to a part of the system that you cannot change, because you need to assign the proper amount of fault as well as just assigning fault, and assigning fault to the part that you can’t change affects the amounts that you assign to the parts that you can change.