Kiped the title from flamingweasel's beautiful, if overly personal node. I hope he doesn't mind too much.
When you grow up, your heart dies; faces blend. They become pieces of crowds in coffee-table books (Where's Waldo? or Magic Eye; take your pick). In time, you see the faces more clearly; you decipher the puzzle. Some of the faces become important; they incite you to joy. And more joy, and inevitably, heartbreak, when you know for sure that the void cannot be filled.