Sure as Eggs is Eggs

Yep! As sure as eggs is eggs, I have tripped over this grammatically skewed expression often enough to wonder about its origin. Today I felt a slight euphoria when I stumbled upon The Art of Science Fiction because through this web detour I finally reached understanding. Sure, the cover art is a pick-me-up in itself but then there are the succinct blurbs and various publishing trivia snippets; pages of glorious procrastination. And then I came to the title of Chapter 7:

As sure as x is x.

Something righted itself in my brain as I read this. Of course!
X = X always, no matter how it is enunciated.