Final answer:
Tom made a "mistake" by expressing pity for Mayella, which was socially inappropriate for a black man towards a white woman at the time, potentially inverting accepted power dynamics.
Step-by-step explanation:
The "mistake" that Tom made in saying he felt "sorry" for Mayella can be interpreted as a reflection of the social norms and hierarchies of the time period in which the story is set. Within that context, a black man feeling sorry for a white woman could be viewed as him assuming a position of superiority, which would have been considered inappropriate and even dangerous due to the racist attitudes of that era. His expression of pity inverted the socially accepted power dynamics and could have fostered resentment or been misconstrued as an overstepping of societal bounds.