Social psychology has found that individuals are more self-focused in times of uncertainty such as new life phases. That is, in times of uncertainty and transition, one's thoughts and actions are more egocentric. In other literature, more narcissistic individuals have been shown to behave differently on social media. Bringing these two streams of research together, we investigate whether and how egocentrism during life periods of uncertainty affect social media behaviors. We identify two life phases with patterns of behavior driven by different types of narcissism. The social needs and heightened sense of egocentrism in these different life phases shape social media behavior, albeit in different ways. We discuss the relevance of these motivational and behavioral differences for understanding social media behavior in different phases of life.