He is willing to die to succeed. If that meant in that moment to outswim his brother he had to drown then he was willing to do it. His brother was limited by hi

He is willing to die to succeed. If that meant in that moment to outswim his brother he had to drown then he was willing to do it. His brother was limited by his fear of death and his subconscious need to still turn around and swim back. He had no concern so was willing to go as long as it took. It just so happened that he was physically fit enough to be able to make the return swim as his brother quit in time.