The best inference that can be made about Daniel's "midlife crisis," which is noted "affectionately" by his friends, is:
C. Daniel is reflecting on the artistic goals and achievements of his youth and wants to feel that happiness again.
This option suggests a nostalgic longing and a desire to reconnect with past aspirations, which is a common theme in midlife crises. The affectionate note by his friends implies they may see this as more of a reflective phase rather than a significant problem.