Carl used to watch the swans. He'd walk along the river. Then every mating season something happened. The swans would start fighting.
What was happening? Carl didn't know what was going on.
The swans must've not known what they were doing either. Because after a few minutes of fighting, mating began.
Carl watched them again the next year. There were pairs of swans and other groups of swans fighting again. Then the ones which were fighting start getting closer. Can you guess what happened next?
The next year was the same. Carl noticed the same swans who fought each other were still together. And still more swans fighting, mating, fighting, mating.
What's this all about? Carl wondered.
Then he realised. The fighting was an act. It had to happen for love to begin. Once swans mate, they're together for life.
The effect of love wouldn't be as strong without the fighting.
It doesn't only happen with swans. Every thing requires its opposite to flourish.
Life requires death. Good requires evil. Feeling full wouldn't happen if you hadn't felt hungry.
What's on the surface doesn't always reflect what's inside.