After the flood, God decides that He would never again destroy the earth, "ki yetzer leiv ha-adam ra mi-ne'urav" – "because the inclination of a person's heart is evil from his youth" (8:21). Human beings' natural, ingrained negative tendencies mitigate our guilt, and thus while we are not absolved entirely of accountability for our wrongdoing, as we are expected to overcome these tendencies, God judges us compassionately and sensitively, and will never again destroy the world on account of our sins.
The Or Ha-chayim, commenting on this verse, draws an intriguing parallel to a halakha established by the Mishna in Masekhet Bava Kama (4:4). The Mishna there discusses the case of "shor ha-itztedin" – a "stadium bull" that kills a person during a bullfight. Normally, an ox that fatally attacks a person must be put to death, as the Torah commands (Shemot 21:28). However, the Mishna states that this law applies only if the ox initiated the assault, as indicated in the Torah's formulation of the law ("ki yigach"). If, however, the ox is provoked to act violently, and kills in reaction to this provocation, then it is absolved of responsibility, so-to-speak, and is not put to death. The Or Ha-chayim writes that God's proclamation of "ki yetzer leiv ha-adam ra mi-ne'urav" reflects a similar concept. We are all, in a sense, "provoked" to sin by the negative tendencies with which we were created. We do not actually initiate our wrongdoing; our sinful actions are the response to the "provocation" of our evil inclination. Of course, as the Or Ha-chayim notes, the analogy is far from precise, since we, unlike animals, are endowed with the power of free will and are thus capable and expected to resist our natural inclinations. Nevertheless, the fact that we are "instigated" to sin, and do not initiate the process, significantly reduces our level of accountability.
The Tolna Rebbe suggested developing this analogy further by noting the question raised by several Acharonim concerning the case of a "shor ha-itztedin." The Gemara (Bava Kama 40b) records a debate among the Amoraim as to whether this bull is acceptable as a sacrifice. Although it is not liable to execution, as it killed in response to provocation, Shemuel nevertheless ruled that the fact that it killed a person renders it unworthy of being offered as a sacrifice to God. The accepted halakha, however, follows the view of Rav, who maintains that since the bull is not held accountable for its actions, and is deemed entirely innocent, it may be used as a sacrifice (Rambam, Hilkhot Issurei Mizbei'ach 4:3). A number of Acharonim, including Rav Elchanan Wasserman (Kovetz Biurim, Bava Kama 33), wondered how this ruling may be reconciled with the halakha established elsewhere (Sanhedrin 80a) that if a pregnant animal killed a person, even the fetus is invalid as a sacrifice. Seemingly, the fetus in such a case bears no more blame for the mother's violent act than a "shor ha-itztedin" bears for his violent act. Why would Halakha disqualify the fetus of animal that killed a person, but not an ox that killed after being provoked?
The likely answer, as the Tolna Rebbe cites from several later writers, is that the fetus is deemed unworthy not because of direct guilt and culpability, but because of its close association with the mother. Irrespective of the well-known halakhic debate as to whether a fetus is legally considered part of the mother's body ("ubar yerekh imo"), a fetus is clearly identified with the mother, such that to some extent, a fetus is formally regarded as a participant in the mother's criminal act. Hence, it is deemed unworthy of being offered as a sacrifice.
Returning to the Or Ha-chayim's analogy, the Tolna Rebbe suggests that the mitigation of our guilt for our wrongdoing depends upon our emotional dissociation from our negative tendencies. As long as we identify with and embrace our negative characteristics, rather than struggling to resist and overcome them, we bear full accountability. If the yetzer ha-ra exists within us as a fetus in its mother's womb, as something we welcome or have made peace with, then we cannot excuse our wrongdoing as the product of "provocation." It is only if we treat our negative instincts as a foreign and hostile force which must be confronted and defeated that we become comparable to the "shor ha-itztedin" such that our guilt is mitigated.