Introduction: In this paper, we wish to elucidate alterations of basic existential and intersubjective configurations in schizophrenia spectrum disorders (SSD) through the phenomenon of Anderssein (“feeling different”). Anderssein is an important yet neglected notion from German psychiatry, referring to a specific sense of feeling profoundly different from others occurring in SSD. Although phenomenological-psychopathological research mentions it as an aspect of the core disturbance of SSD (namely, “self-disorders”), the phenomenon has not yet been explored in empirical or theoretical detail. Method: We present material from a phenomenological-empirical study on the mode and onset of psychosis based on qualitative interviews with 25 patients with SSD. Results: Most of the participants in our study report having felt fundamentally and often ineffably different since childhood and articulate it as a sense of existing “outside” of the shared reality. Intersubjective reality appears progressively unreal or inauthentic, and simultaneously, the patient’s intimate, subjective sphere is permeated by an alien otherness. Importantly, this outside position should be understood carefully as it is often accompanied by the sense of being invaded by social rules, other people’s thoughts, or emotions. Incipient psychosis is described as a gradual extension of precedent alterations of the structures of (inter)subjectivity. Conclusion: We conceptualize the ontological feature of Anderssein as an altered “being in-between” – that is, some sort of halting of the dynamic movement between particularity and intersubjectivity. Finally, we discuss the critical implications of these results for research into the “onset” of schizophrenia.