Final answer:
Atticus takes on a case he cannot win to stand up for justice and to teach his children the importance of moral integrity, despite the racial prejudices of the time.
Step-by-step explanation:
When Scout asks Atticus why he is taking on a case that cannot be won in To Kill a Mockingbird, Atticus's response suggests that he believes it is important to stand up to the right even though in the face of certain defeat.
Atticus feels strongly about justice and equality, and his decision to defend Tom Robinson is a reflection of his moral convictions, despite the pervasive racial prejudices of the time.
By undertaking this case, he demonstrates his commitment to fighting against injustice and teaching his children about the importance of integrity.