Musar על בבא קמא 6:3

When the Torah discusses legislation involving damages caused by an animal's horn (Exodus 21,35), it is a rule of thumb that an animal which had a blameless record, was never aggressive, is held responsible (its owner) for half the damage it has caused. If, however, the animal had a record of causing damage, its owner is assessed the full value of any damage it has caused. When a human being causes damage he is always considered as having a record of aggressiveness and is therefore always held responsible for the total damage he causes. This all dates back to original man who had caused severe damage to this world, so that all human beings who came after him must consider themselves as having been forewarned. G–d had warned him that "on the day you eat from it you will become mortal." Adam had been fully awake at the time the serpent seduced him; this is why he could not plead extenuating circumstances. He also sinned while asleep, since, during the one hundred and thirty years that he did not cohabit with his wife he emitted semen nocturnally, which in turn was converted into all kinds of destructive spirits, as we have explained elsewhere. This was all due to his having absorbed pollutants emitted by the serpent. As a result, man is held fully responsible for damage caused by him both while awake and while asleep. When we speak about man as being מועד לעולם, forewarned concerning any sin he commits, and therefore fully responsible for his actions, this means that he pays the full penalty, mortality, for his transgressions. This mortality is passed on from generation to generation.