The pioneering identity researcher Erik Erikson first proposed the term “ego identity,” which he conceived as an enduring and continuous sense of who we are. The ego identity allows a person to merge all the different versions of oneself (the parent self, the career self, the sexual self) into one cohesive whole, so that when unexpected disaster strikes, there's a stable sense of self.
Of course, major life upheavals cause many people to explore and redefine their identities. This reappraisal can occur at any stage of life, though people think that adolescence is the primary identity-forming period. Yet, today, many people in their late twenties and older are still trying to figure it out. As a person grows older, the overall trend is toward identity achievement, but divorce, the death of a loved one, retirement, and other shake-ups can make one question the very concept of "Who am I?" and "Who do I want my future self to be."