At the beginning of The Outsiders, young narrator Ponyboy Curtis feels isolated from the members of his gang, his brothers, and society at large. His intellectualism and his love of movies, books, and nature aren't really appreciated by the gang, or so he thinks. Pony's status as a Greaser also makes him feel like an outsider, locked out of opportunities that wealthier kids enjoy, and unfairly judged by teachers and other authority figures. Things are looking grim for Ponyboy and the other guys in his gang. But, as the story progresses, Ponyboy becomes more aware of connections between Greasers and Socials and between his friends and loved ones. In the process of writing down his story, he learns the powerful sense of connection that can come from reaching out to other "outsiders," and from bringing their struggles to light.
Darry is isolated by his decision to care for his younger brothers, but the love and satisfaction he gets from doing so more than makes up for it.
When Johnny dies, Dallas feels completely isolated from the rest of humanity.