Nostalgia
Once a butterfly got so homesick, he wanted to go back in his cocoon. But he couldn't, for his beautiful wings were fairly large. He tried crawling back in, oh try hard he did. His wings hurt, blocked his way. So obsessed, so desperate he got, that he chewed his wings off. He wasn't a butterfly anymore. Nor was he a caterpillar. But he was back in his cocoon, Never to get back out again.