One connection between the four works is how individuals have to assert their own voice in the face of a controlling external reality. Liesel feels compelled to display a voice of compassion and care despite an external condition of Nazism that espouses quite the opposite. Juno feels driven to embrace her own voice, despite the fact that pregnancy and the world around her has become so complex. Ada must follow her voice, one that cannot be readily heard by the world around her. Holden feels compelled to use his voice in a world of "phonies" and people around him that fail to acknowledge his condition.
In each of these settings, I think that one can find how the individual must withstand the forces around them that seek to silence their voice. External reality is pressing down against these characters. Within such a condition, these individuals do not capitulate to society, but rather maintain their voice and seek to enhance it while the world only wishes to stifle and silence it. These conditions of being are where one finds connection between all four works.