The narrator then thinks back to the last time he saw his mother alive, just before he went off to war most likely fought in Korea.
They talk about suffering. We try to protect ourselves and those we love, to make them feel safe as well. Sonny was withdrawn and quiet, while their loud-talking father pretended to be big and tough.
The narrator describes his father, a drunken man, who died when Sonny was fifteen. It then flashes forward, and he talks about Gracie and her polio affliction. He has a heroin addiction, which led him to jail, but because of his passion for jazz, he became a musician.
Music is the only way for Sonny to express himself.
Here, sonny means that it takes courage to resist the temptation of trying heroin once you have tasted it because it makes one feel high. Thinking of his brother reminds him of his students, who face limited possibilities in a hostile world.
He functions as a kind of father figure for Sonny. Reading example essays works the same way! Eagleman, David.