Well, technically, there's a limit to how much we know. Maybe there's a giant meteor headed for Earth in NASA's blindspot, or maybe the heretofore unknown theory of Tectonic Substrate Implosionment will cause gravity to suddenly invert and cause the Earth to explode.
You never know.
I make sure to spend my life savings on toothpaste every year, just in case. After all, there's a slight probability that with another few pounds of toothpaste weighing down the Earth's tectonic plates, we could avert disaster.