I am now first in my initiate class. I may have chosen Dauntless as a haven, but I'm not just surviving here, I'm excelling. (2.173)
Four made the right choice, choosing a faction that values physical strength. As he trains obsessively, his strength grows exponentially.
"Dauntless has always embraced a spirit of competition," Eric says. "Competition makes us better; it brings out the best, strongest parts of us." (3.283)
Kelly Clarkson would make a good member of Dauntless. "What doesn't kill you makes you stronger," could be the Dauntless motto, verbatim.
"I would improve Dauntless by fostering true bravery instead of stupidity and brutality," I say. "Take out the knife throwing. Prepare people physically and mentally to defend the weak against the strong." (3.292)
Four has the complete opposite idea of Eric. Eric wants to be the type of person who uses his strength to prey on the weak, while Four wants to protect them… until they're strong enough to take care of themselves.
"Hey," [Tris] sighs. "We got through it." […] "You got me through it," I say. (4.542, 4.544)
Tris's bravery and strength under pressure is contagious. Without her, solid as a rock, Four would fall apart when facing his worst fears.
As she tumbles over the side, I grab her arms to steady her. She's small, and thin—fragile-looking, like the impact with the net should have shattered her. Her eyes are wide and bright blue. (5.15)
Tris's about-to-break physical appearance is supposed to emphasize how strong she is. She doesn't look strong, but she is! That makes us perceive her to be even stronger than she actually is.