Why does Atticus think he can't win Tom Robinson's case?

understands that winning the Tom Robinson case is virtually impossible due to the systemic
racism and prejudice that is prevalent throughout Maycomb, Alabama. In ,asks her father if he
has a chance of winning the case, and Atticus says, "No, honey"
(Lee 48). Scout then asks her father why he is even trying, and Atticus says,
"Simply because we were licked a hundred years before we started is no reason for
us not to try to win" (Lee 48). Later on, Uncle Jack asks Atticus if he has a
chance of winning the case, and Atticus says,

"It couldnt be worse, Jack. The only thing weve got is a black mans word
against the Ewells. The evidence boils down to you-didI-didnt. The jury couldnt possibly be
expected to take Tom Robinsons word against the Ewells'" (Lee 55).

Atticus realizes that the jury will not accept Tom's testimony as
truth for the simple fact that Tom is an African American. In 1930s Alabama, segregation was
commonplace, and Jim Crow laws were enacted to separate and discriminate against black people.
The Post-Reconstruction era promoted systemic racism
throughout the South and Atticus is essentially challenging the entire culture by defending a
black man. The jury could not possibly rule in favor of Tom and subject themselves to the
cultural taboo of favoring "Negroes."