It just came to my mind if we actually know them. Think about water, it gives us life but the other nature of it can cause disasters. The same is with fire. They have the power to clear our existence all at once. What I mean to say is that we don't know someone completely, there's some part of a person that's a mystery. That comes to the surface in the extremes. I mean like there's a part of me that no one knows. No one knows what's the dead end of knowing someone. Our entire lives revolve around socializing and interaction but it's never enough. There's always more to things that are beyond our knowledge and it will always be that way. Imagine a human overpowered by anger and revenge, they will then have the power to destroy the world. Yes, terrorism I mean. That particular nature will be triggered only by a very rare incident that happened. Robert Frost's one of the most popular poems "Fire and Ice", has a mention about how the world will end either because of hate or desire. I believe that we are still unknown to a part of us for good.