As sure as eggs is eggs.

[david niven]

We all know what the phrase means but where did it come from?

[xyzzyplugh]

I think it is a progression of 'as sure as X is X'

[Quizmonster]

In olden times, there were lots of proverbial-type phrases involving eggs. People were said to be 'as like as two eggs' (Shakespeare 1611) or were advised not to 'put all their eggs in one paniard' (1666). The earliest-recorded appearance of 'as sure as eggs are eggs' was in a dictionary of slang published in 1699. The 'eggs is eggs' version is just a more modern variation. It's pretty clear that the basic idea is at least half a millennium old, in other words, if it was published as slang in the 1600s.

[j2buttonsw]

So David, reports of your death were greatly exaggerated.