Have you seen all of nature to affirm without any doubt that something doesn't exist?
Besides, just because the overwhelming majority of something is a certain way doesn't mean it can't exist in another way. For instance, while all known beaches organize themselves as flat expanses of sand, there is still a probability that a wave comes along and spontaneously forms a sandcastle, albeit a vanishingly small one. Nobody's ever seen it, and probably nobody ever will, but it's possible. That's just math.