Though there may be some truth in what yasaka said, that’s not the way to go about making someone realize that. Mitsumi is who she is because of how she was raised and the relationships she has with people around her, and there is completely nothing wrong with that. In fact, the way she can be so optimistic and see the good in everybody is because of that!
I totally understand Mitsumi’s thoughts and rationality. Everything SHOULD have gone the way she was describing, but unfortunately it’s not a perfect world and people don’t always behave the way you expect/want them to. However, this realization is a big part of maturing and I just love love love how the author displays the transition from youth to adulthood through these conflicts. Beautiful masterpiece, this manga