Wow, that was so much better than the 7 page article, thanks! I understand what the article was about now. I kept getting lost in the side stories. How is it

Wow, that was so much better than the 7 page article, thanks! I understand what the article was about now. I kept getting lost in the side stories. How is it that people can predict when the ETFs need to roll their contracts? And how do they make money from knowing this?