Comment by robgibbons

SSI's were my first foray into "backend," if you can even call it that, sometime around the year 2000. Some benevolent commenter on Slashdot gave me the tipoff, and my growing frustration with copy-pasting HTML snippets between pages was henceforth a thing of the past. Then came PHP, Python, et cetera, and the rest is history.

Amazing how such a simple mechanism can remain useful even decades later.