User blog comment:256k/(SPOILERS) The 4º Wall / The other city theory/@comment-5995523-20131018161816/@comment-5995523-20131020045906

True, but Eren also needs some motivation as well, which is why in a previous chapter, Ymir pointed out his powers are not as reliable in comparison to those who had the titan shifting abilities longer than him. We'll have to find out when we see the basement.

At this point, I still think Mikasa is the bigger threat as she's much more reliable with her military training. Even Ymir saw how strong she was and wanted to attack her in order to protect Historia.