I was reading @diam-etrical's inspired by The Hunger Games AU (which by the way is amazing and you should go read it if you haven't already) and had some thoughts on Peeta and Armin as mirror characters, mostly in terms of what this comparison brings to Armin's characterization (since I obsess over aot at the moment), which I decided to share with y'all.
So Armin is and isn't Peeta Mellark. They're both highly intelligent, skilled orators and perceptive. They have the ability to read people and to sway them in their favor. Also, especially in comparison to their more self-centered love interests, they both have a strong sense of morality.
However Peeta's thesis in the beginning of THG (which follows him throughout the story and shapes his character arc) is the line "If I'm going to die, I want to still be me," which is fundamentally antithetical to Armin's maxim "someone who can't sacrifice anything, can't change anything" (in the context of Erwin losing his own humanity for the greater good). What's more, Peeta's story proves Armin's philosophy wrong. Peeta very clearly defines the outcome of the games by his commitment to his beliefs and principles, by preserving what makes him human and when that is lost (in mockingjay), we as readers but also katniss as a character in the story, mourn this side of him and understand it to be a loss too great.
The thing is though, Armin's story also kind of proves him wrong (to a degree). On one hand, Armin is incapable of letting go of Eren and the image of him he remembers from his childhood: the strong, brave Eren who fought for justice. Ultimately, this inability to accept that Eren has changed is what clouds his judgment concerning Eren's motivation until it's too late. On the other hand, Armin ends up disagreeing with Eren that the Rumbling was for the better (I'm disregarding the "thank you for becoming a mass murderer" line because I interpret it to be for Eren's benefit--meaning that Armin was trying to comfort his best friend at that point). His last actions in the story are about him being opposed to Eren who deemed the outside world worthy of sacrificing for the greater good of the Paradisians. Therefore, even Armin himself by the conclusion of the story is not willing to sacrifice everything.
And yet, Armin is not entirely wrong. Armin makes great sacrifices to achieve peace and to do the right thing. He is willing to risk his life, his friend's lives, the chance to be with the woman he loves, Eren (both in the sense of Eren's life and in the sense of Armin's idea of Eren). Armin is even willing to besmirch his own reputation (in his eyes) by naming himself Eren's killer; it is a burden he's willing to bear for Mikasa, but also to pacify the Marleyans. These sacrifices are crucial in order to prevent perpetual conflict.
In the end, Armin's quote is more about compromising than about giving up your humanity and empathy.
So the main takeaway from paralleling these to characters, at least for me, is that there are things that are worth sacrificing (toxic beliefs, your personal comfort, an oppressive status quo) and things worth preserving (ideals, life, love). Violence may be necessary to enact change, but in order to maintain the positive impact you created, you need to be able to drop your weapons and find common ground.