Wesley Autrey, a black construction worker, a Navy veteran and 55-year-old father of two, didn’t know the young man standing beside him. But when he had a seizure on the subway platform and toppled onto the tracks, Autrey jumped down after him and shielded him with his body as a train bore down on them. Autrey could have died, so why did he put his life on the line — literally — to save this complete stranger?