Comment by SAI_Peregrinus

Royce's original "Waterfall" paper[1] is significantly more iterative & agile than Scrum! It's outdated since at the time (1970) programming was done mostly on paper & then run later on a mainframe or special-purpose computer, but many of the core ideas still hold true for modern programming environments.

Of course many of the organizations that claimed to be implementing Waterfall omitted the iterative steps, then wondered why it didn't work. That also happens with "Agile" processes. Sticking to the waterfall analogy, it's like if you stopped the evaporation & precipitation cycle that refills the upstream aquifer & wondered why the waterfall stopped flowing!

[1] https://www.praxisframework.org/files/royce1970.pdf