References have meanings.
One of the best lessons from my high school creative writing class was about using allusion to impart meaning. The teacher read us an excerpt from a short story about a young girl who was sunbathing naked on an island. When a boat full of guys came into sight in the distance, she stood up, spread her arms like Jesus, and buzzed around like an airplane so that the boys could see her butt.
What, the teacher asked us, did Jesus and an airplane have to do with anything in that scene? What was the point in making the reader think about Jesus and airplanes if they contributed nothing to the story?
If someone, fictional or otherwise, says "that dude and his problems are none of my business", what they're saying can be taken at face value. It may even be true! If, however, they tell you "I'm not my brother's keeper", what they're saying is "Hey, remember that dude in that story who murdered his brother, then tried to lie about it to an omniscient God? This is me doing my impression of him!".
It's kind of like how a tattoo that says "Be yourself" can be taken at face value, but a tattoo that says "To thine own self be true" actually means "I'm a useless narcissistic fop who doesn't realize he's in a scene that's being played for laughs, and at some point I'm going to intervene in a domestic disturbance and get stabbed". Which, y'know, is probably accurate.