In my humble opinion, it is clear and obvious that with regard to a person who causes damage, there is no room at all to suggest that the basis of liability is failure to guard. There is simply no need for that. Only in the case of property that causes damage is there room for such a possibility, and that is in order to explain the relationship between the damaging act of one’s property and its owner. Why should he pay for what his damaging property did? Even after the Torah’s novelty that he must pay, what is the underlying reason behind the Torah’s law? Is it enough that it is his property—is that already a sufficient connection to impose on him liability for the damage his property caused? Or perhaps that is not enough to obligate the owner; rather, liability exists only because the owner has a duty to guard his property so that it not cause damage, and he failed to guard it, and as a result the damage was caused. That is the reason linking the owner to the damage. But in the case of a person who causes damage, where it says, “If a man strikes an animal, he shall make restitution,” it is obvious that if this is defined as the act of the person who caused the damage, then of course he must pay, since the Torah decreed that where there is a person causing damage, he must pay. There is no greater connection than the fact that he himself did the damage. So what sense is there in saying that his liability is due to failure to guard his body from causing damage? What is lacking in the fact that he performed the damaging act?
Indeed, they have already brought proof from the language of the Talmud: “A person’s safeguarding of his body is upon him,” and this is included in the common denominator that “their way is to cause damage and their safeguarding is upon you.” Rabbi N. P. explained this: an awake person and a sleeping person are two different grounds of liability. An awake person is indeed as stated above: he is liable for his actions as a person of understanding who acts; there is someone here performing damage, and he is liable. But in the case of a sleeping person, who at that moment has no awareness and causes damage without intent, there is no room to obligate him for his actions as an actor, because without awareness there is no acting person here. Rather, in that case we come to obligate him on the basis that the safeguarding of his body is upon him—he should have guarded his body from causing damage while asleep, etc., and this is not the place to elaborate.

That is exactly what I brought from Rabbi Shlomo Fischer. In the case of someone asleep, it is not his act; rather, it is like his property. But if so, we should have exempted him in a case of duress, since regarding property, if the owner is under duress he is exempt. Seemingly, this proves that his body is indeed not identical with himself, but it is closer to him than his property is. His body is something in between his very self and his property. According to this, it may perhaps indeed be possible to say that even when an awake person causes damage, it is by virtue of the duty to guard his body.