Short answers, pulled from the story.
In existentialism, authenticity is the degree to which a person takes ownership of their choices and identity, acting in recognition of personal freedom and responsibility rather than deferring to social roles, norms, or external authorities. Philosophers including Søren Kierkegaard, Martin Heidegger, and Jean-Paul Sartre each developed distinct accounts of what this ownership requires.
Geworfenheit is a German term meaning "thrown-ness." It describes the condition of having been thrown into an absurd world, without predetermined values or meaning, not of one's own making. Existentialist philosophers used it to identify the external forces and influences a person must confront in order to live authentically.
Kierkegaard argued that personal authenticity depends on inwardness and a subjective relationship to truth, particularly in matters of faith. In Practice in Christianity (1850), he used the image of a preacher standing before God to argue that authentic existence requires standing alone before one's commitments rather than sheltering in social convention or institutional religion.
Fromm considered any behavior authentic if it comes from personal understanding and genuine approval of its motivations, even if that behavior conforms to social norms. He called Sartre's emphasis on freedom from external restraint "the illusion of individuality," contrasting it with what he saw as genuine individuality arising from informed, self-aware motivation.
A poseur is an artist or band who copies the dress, speech, and surface mannerisms of a musical subculture without understanding its artistic philosophy, sociology, or value system. In genres like punk rock and heavy metal, authenticity rests on three bases: long-term dedication to the music scene, historical knowledge of the subculture, and personal integrity in artistic choices.
The authenticity paradox refers to the tension social media users experience between expressing personal values and meeting social expectations to share commercially popular values. By curating images and performing experiences for an audience, users convert genuine experiences into advertisement, producing an image of authenticity rather than the condition itself.