That's a fair question and a valid one.Makes some sense? Well, in one sense, it seems to say that there is no way to escape the evil you know, because you can't trust anything new. Seems pretty dismal to me.
But even worse, I can understand the idea of "an evil one knows," but how do you decide that this other thing, the "evil that has yet to be seen," is evil -- if you haven't seen it?
One has to assess from what evil this evil has evolved.