Quote 1
"Sometimes they do. And sometimes new fears replace them." His thumbs hook around his belt loops. "But becoming fearless isn't the point. That's impossible. It's learning how to control your fear, and how to be free from it, that's the point."
I nod. I used to think the Dauntless were fearless. That is how they seemed, anyway. But maybe what I saw as fearless was actually fear under control. (18.94-5)
Here's Dr. Four (not really a doctor), laying out his theory about fear and acting brave, which is very much like what he said about his fear of heights: you act in spite of the fear. Tris notes that this "maybe" is what's going on with the Dauntless. Is it strange that Tris keeps thinking about fear as "maybe" this and "maybe" that? (Or is it weird that, in the middle of his speech about fear, Four puts his thumbs through his belt loops, like he's just hanging out? Apparently, he's not afraid of Tris.)
Quote 2
"My first instinct is to push you until you break, just to see how hard I have to press," he says, his fingers squeezing at the word "break." My body tenses at the edge in his voice, so I am coiled as tight as a spring, and I forget to breathe.
His dark eyes lifting to mine, he adds, "But I resist it."
"Why..." I swallow hard. "Why is that your first instinct?"
"Fear doesn't shut you down; it wakes you up. I've seen it. It's fascinating." He releases me but doesn't pull away, his hand grazing my jaw, my neck. "Sometimes I just...want to see it again. Want to see you awake." (24.92-5)
Okay, you may beg to differ here, but this makes us look at Four a little nervously. On the plus side, he does resist his urge to push Tris until she breaks, so, yay. What a gentleman. But his first comment is more than a little creepy. Still, aside from the fact that he himself is a bit scary here, what he teaches Tris about fear is just as important. He's showing her that fear can make her better, more alive in some ways.
Quote 3
"The leadership," he says. "The person who controls training sets the standard of Dauntless behavior. Six years ago Max and the other leaders changed the training methods to make them more competitive and more brutal, said it was supposed to test people's strength. And that changed the priorities of Dauntless as a whole. Bet you can't guess who the leaders' new protégé is."
The answer is obvious: Eric. They trained him to be vicious, and now he will train the rest of us to be vicious too. (18.108-9)
Society isn't a static thing. We don't know how long the five factions have been set up, but we can see that things are changing (like with Erudite hating Abnegation). Even within the factions, things are changing, as Four makes clear here: the Dauntless leadership has decided to take this whole "let's be brave" idea in a new direction.