Typically, landmark cases reflect the everchanging views of norms in society overtime and usually demonstrate a shift in opinion.
For example, Plessy v. Ferguson marked a time where segregation and racism was viewed as a norm and was not uncommon to see in a society recovering from the Civil War. With the decision on Brown v. Board of Education, it showed that society began to reject the vile tradition of segregation and shift toward the view that all men are created equal.
Another landmark case is Roe v. Wade. It is typically viewed as a landmark case for women's rights, demonstrating how society's views on a woman's rights and views on abortion changed.