An excuse defense is a legal argument that seeks to absolve a defendant of liability by asserting that they should not be held responsible for their actions due to specific circumstances that negate culpability. This defense operates under the premise that while the act may have been committed, the individual lacked the necessary mental state or was unable to make rational decisions due to external pressures. It highlights the complexities of human behavior and acknowledges that not all actions can be fairly judged in the same manner.