How we cite our quotes:
I stare into my own eyes for a moment. Today is the day of the aptitude test that will show me which of the five factions I belong in. And tomorrow, at the Choosing Ceremony, I will decide on a faction; I will decide the rest of my life; I will decide to stay with my family or abandon them. (1.9)
This is the big choice that Tris faces; and luckily for her, she has some help in making that choice. Before she decides, she gets to go through the Sorting Hat—er, we mean the aptitude test. But even with that aptitude test, notice how big this choice is: it gets three repetitions of the phrase "I will decide." That's how we know it's important.
At the Abnegation table, we sit quietly and wait. Faction customs dictate even idle behavior and supersede individual preference. I doubt all the Erudite want to study all the time, or that every Candor enjoys a lively debate, but they can't defy the norms of their factions any more than I can. (2.7)
Everyone in a faction does the same things because they're in that faction. And yet Tris recognizes the possible separation between the "individual preference" and "Faction customs." Is Tris the only one who feels like making a non-faction choice? (Probably not, but it can feel like that sometimes.)
"Beatrice," he says, looking sternly into my eyes. "We should think of our family." There is an edge to his voice. "But. But we must also think of ourselves."(4.64)
Tris isn't the only one who wants to express her individual choices against the faction norms (see above). Even Caleb, the perfect Abnegation, does something very non-Abnegation here. And we know this is a big issue because Tris keeps breaking in to tell us it's a big issue: Caleb's eyes are stern, his voice has an edge. If this were just a boring line of dialogue, Tris probably wouldn't be noticing all these little physical clues.