This paper provides a comprehensive view on a concept of the unknown self (UKS). The manuscript covers the origin of UKS, conditions of its existence, its associations with the known self (considering paradoxicality of these associations), subjectivity of its pursuit and disclosure, its impact on reaching self-identity and self-transformation. An original starting definition of UKS is introduced; UKS is defined as one’s awareness of not knowing themselves. UKS is presumably overcome via reflection, relationships with others and productive actions. The study employed personological methods integrating thereby the theoretical hermeneutic (cultural) model of UKS, empirical backgrounds to studying UKS, a new “Unknown Self Scale”. The authors justify a paradox of the relationships between UKS and the Known-Self. The paradox is treated as a particular balance of binary oppositions, wherein each opposition is necessary for its counterpart to exist, both are equivalent to each other, have properties determined by their mutual associations, be mutually consistent in a constructive manner. Several aspects of UKS, given previously insufficient attention paid, were highlighted in the paper including UKS and interpersonal relationships, hypostases of UKS, its content, UKS under one’s opportunities and potentials, age changes in UKS, UKS and significant others, UKS within extended interpersonal space, UKS in the structure of self-concept, UKS as an attribute of self-identity and self-disidentification, motivation to search for and uncovering UKS, cultural and individual sources of “knowing about not knowing themselves”.