- Red cars = "follow the red path, follow your passion: choose Anna!"
- Argyle sweaters = living a (safe, risk-less) life behind the scenes, as an observator of the world rather than as a participant in the world.
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Joe Satriani - "Always With Me, Always With You"
http://youtu.be/VI57QHL6ge0
It means lack of differentiation. Everything is the same, no individual choices, just conformity to more of the same. The fact that Nemo's mother (which looks older) didn't recognised him and she had a different son that lived with her still shows what happens if a child does not brake away from parents.
They never become unique individuals and they remain copies of their parents.
Nemo, regardless of what choices he made was unique, that's why he did not actually exist in that world of more of the same.
The movie is a masterpiece but that part especially blew me away!
You got good explanation here.
Excuse my English, I am French-Canadian