Their childhood and them just being kids
Atticus knows he probably won't win but he does this anyways to uphold his sense of self-respect and justice
it isnt usual for white lawyers to do their best for 2 reasons i believe:
1) black people are usually convicted so its almost possible to defend them even if they are innocent
2) like a lot of people there were also some racist lawyers
It is a matter of individual will power and the ability to fight against the odds.
Explanation:
While the way one person responds to adversary conditions has a lot to do with their situation of privilege against the adversary, it also has to do with the way they are conditioned as people.
Some people react better to such conflicts because they are either used to facing such high pressure situations or have mental fortitude for it.
It is also to be considered however that different things affect people differently and there is no way of knowing how one would react to such situation when it comes to it.