"part of you wants someone to notice that you're missing, so that you can be not just doing something important but be a hero about it."

=> Besides the ego, there's also a cultural component. My Finnish friends tend to excel at leaving without saying goodbye or hugging, not because they have weaker ego but because that's a part of their culture. That said, in my culture (South Korea), your saying nothing when leaving will immediately strike people as socially incorrect or weird to say the least.