When Tobias Eaton leaves Abnegation, he doesn't just leave his father behind. When his little sister follows him to Dauntless, she knows that it's going to be tough. But only Tobias knows the full extent of the danger she's in. He vows to do what he can to keep his sister safe and happy - at any cost.
"The stars keep shining, unaware of the internal battle that he keeps fighting, that he's always fighting. They're the only ones who haven't left him, after all these years. … He's always alone, isn't he? At the end of the day, it's always him against the world. Just him. … Will he ever find a place - or a person - to call home?"