This work examines some of the epistemological and ontological conditions of the deep self-knowledge that is demanded by the Delphic motto gnothi seauton (know thyself!). The guiding questions are: what is the 'self' that deep self-knowledge is of? What are we such that we can ask deep and puzzling questions about our life-plans, our self-conceptions and the meaning of our lives? Can we know ourselves as we really are, or only under a certain description which conceals as much as it reveals? What is the nature of the relation between self-knowledge and (personal or inner) reality? The central thesis that is defended is that a person is to a certain extent a self-defining and self-forming being by virtue of his self-knowledge; fundamental ch...