"In 'Transcendence of the Ego', Sartre argues that when one turns inward to examine one's own states one creates a new object, the ego, that had previously not existed. For Sartre, there is no independent subject of the classical kind, access to which is secured, as Descartes believed, by introspection, an inspection of the mind. Consciousness cannot know itself independent of its relation to things. Far from being a privileged form of self-knowledge, introspection is for Sartre largely deceptive."
Robert Bersconi, How to Read Sartre.