Physics relies on the fundamental postulate that the universe follows certain laws which, because they are laws, are rational. It remains to find out exactly what those laws are. If one could find out what those laws were, the universe would be rationally explicable.
But human beings are also in the universe. That is, they are not apart from it. And we know that human beings have irrational impulses, both emotional and intellectual.
Because of that, can we say that the universe can not be (wholly) rationally explicable since human beings are not.