The correct answer is evidence of mental incapacity. In legal contexts, the presumption of willfulness implies that a person intended the consequences of their actions. However, if a person lacks the mental capacity to understand their actions or the nature of their conduct due to a cognitive disorder or impairment, this can effectively rebut the presumption of willfulness.
Mental incapacity refers to various conditions that affect a person's ability to think clearly, understand reality, and make rational decisions. When individuals are deemed mentally incapacitated, the law recognizes that they may not have the necessary intent or volition to commit an action willfully. This understanding is critical in contexts such as criminal law, where intent plays a significant role in determining culpability.
Concerning the other options, while proving an act was performed by accident could provide a defense, it typically does not directly address the presumption of willfulness as effectively as mental incapacity does. Showing intent to harm contradicts the premise of rebutting willfulness, as it implies the individual did indeed act willfully. The notion that none can rebut the presumption does not hold, as legal principles permit various defenses, including that of mental incapacity.