I find it so amazing that, while we understand how gravity works to some extent, we still don't really know where it comes from or why it works the way it does. Yet, it is one of the most important forces in the universe, at least from our perspective.
Without gravitational energy, we wouldn't have a planet, because the matter that makes up Earth would go flying away with nothing to hold it together. It also wouldn't orbit the sun, so we wouldn't have the day and the seasons the way we do.
It's just incredible that it's such an important thing and we don't understand where it comes from.