I have something interesting to share from the new guidebook interview
>That's the scene in Vol. 18 where they talk about the sea!
>Isayama: Yes. But unlike Armin who fought in order to see the sea, at that time Eren is actually not that crazy over the sea. Eren and Armin became friends when they were kids because they share a common dream which is "the outside world", but the roots of that dream are slightly different in the first place. Armin's desire to "see the sea" stems from intellectual curiosity, while Eren felt anger because "the sea exists but we don't have the freedom to see it" and isn't interested in the sea itself. In addition, the various situations Eren got caught up in so far have changed many things, and the sea also went to the back of his mind. The difference between them becomes clear and Armin got a shock which was depicted in that scene in Vol. 18.
>Is that so?!
>Isayama: When they arrived at the sea, Armin held a shell which symbolizes "an object that only exist at the sea" and told Eren to "look at this". However, Eren didn't turn to look at that. "The neglected shell" left all alone in Armin's hands signifies "the end of the dream" or "the end of youth". Something like...3 friends, who were always together, embarking on different paths after graduating from high school.