So, in episode 55th of Attack on Titan
When Levi is about to inject Erwin, he hears him say, "professor, how do you know there isnt people on the other side of the walls". Levi reminds that Kenny Ackerman when dying told him that everybody has to be drunk with something. And then he later says he chose Armin because they pushed Erwin to be a demon.
I dont see the relation among all these situations / thoughts. Why Levi chose Armin instead of Erwin?
This is just how I interpret it based on what I know.
In Chapter 72, when Levi and Erwin are talking about the plan to defeat the Beast Titan, it was revealed that, to quote from the wiki,
He cared more about discovering the secrets hidden in Eren's basement, and finally proving his father's theories correct, than he did about retaking the lost territory of Wall Maria. His dream of understanding the world was so strong that he confessed to Levi that he considered it more important than the victory of humanity.
Levi was reminded of Kenny Ackerman who, while dying, told him that everybody has to be drunk with something... This is when Levi realizes that what Kenny said applies to Erwin. Erwin was drunk on curiosity to understand the world than to save the people within the walls. If he would choose Erwin, Erwin would prioritize his dreams rather than their goal of saving humanity.
And then he later says he chose Armin because they pushed Erwin to be a demon. Had Erwin's circumstances been different, had his father not been killed and if he was able to pursue his goals of understanding the world without having to worry about being arrested, he would probably have been a researcher or someone other than a soldier. Levi understands that Erwin only wanted to answer the questions he had about the world. It was never really his desire to become a soldier or be handed the position of someone who should save humanity. If he chose Erwin, sure, Erwin's questions would be answered but it would likely doom humanity as Erwin's goal stops at answering his questions and proving his father right. In an episode of the latest season, I seem to recall Levi asking Erwin what happens after they find the truth in the basement, to which Erwin replied 'I don't know'.
Erwin sacrificed many lives for his ambition whereas Armin sacrificed his life with the intent of Eren achieving their ambitions. Armin was willing to give up his life and prioritize humanity's survival so long as Eren, the one he promised to see the sea with, can achieve their dream for the both of them. Erwin, however, was willing to give up the lives of his subordinates in order to achieve his dream, which only is about answering his questions and proving his father right.
well, my interpretation is that erwin’s main goal was only to find out the truth of the world, by going to the basement. that his dream ends there. he himself stated that he didn’t know what he would do after he accomplished his dream, and so even if levi gave him the injection, he wouldn’t have any motivation to continue after visiting the basement. this ties in with kenny’s last words, which levi took into consideration and was a huge factor in his decision. kenny said that “everyone needed to be drunk on something to continue” in other words, they needed a goal. erwin was so close to reaching that goal, which was also why he hesitated so much to give up on it. + it was his time to rest
on the other hand, armin’s dreams stretch much further than erwin’s. armin said that the first part of his goal was to see the sea, “lets START by seeing the sea”, showing that even after visiting the basement, he would go on to reach his goal, unlike erwin. thus, levi was looking into the long term, and chose based on who would have the drive and motivation to lead the survey corps the best in the future.
